Tool doesn't work on non git repositories.

ember-cli-update doesn't work on my Mercurial repo:

```
> DEBUG=ember-cli-update,git-diff-apply ember update
ember-cli-update npm info ember-cli versions --json +0ms
ember-cli-update [
ember-cli-update "0.0.0",
ember-cli-update "0.0.1",
ember-cli-update "0.0.2",
ember-cli-update "0.0.3",
ember-cli-update "0.0.4",
ember-cli-update "0.0.5",
ember-cli-update "0.0.6",
ember-cli-update "0.0.7",
ember-cli-update "0.0.8",
ember-cli-update "0.0.9",
ember-cli-update "0.0.10",
ember-cli-update "0.0.11",
ember-cli-update "0.0.12",
ember-cli-update "0.0.13",
ember-cli-update "0.0.14",
ember-cli-update "0.0.15",
ember-cli-update "0.0.16",
ember-cli-update "0.0.18",
ember-cli-update "0.0.19",
ember-cli-update "0.0.20",
ember-cli-update "0.0.21",
ember-cli-update "0.0.22",
ember-cli-update "0.0.23",
ember-cli-update "0.0.24",
ember-cli-update "0.0.25",
ember-cli-update "0.0.27",
ember-cli-update "0.0.28",
ember-cli-update "0.0.29",
ember-cli-update "0.0.32",
ember-cli-update "0.0.33",
ember-cli-update "0.0.34",
ember-cli-update "0.0.35",
ember-cli-update "0.0.36",
ember-cli-update "0.0.37",
ember-cli-update "0.0.38",
ember-cli-update "0.0.39",
ember-cli-update "0.0.40",
ember-cli-update "0.0.41",
ember-cli-update "0.0.42",
ember-cli-update "0.0.43",
ember-cli-update "0.0.44",
ember-cli-update "0.0.45",
ember-cli-update "0.0.46",
ember-cli-update "0.0.47",
ember-cli-update "0.1.0",
ember-cli-update "0.1.1",
ember-cli-update "0.1.2",
ember-cli-update "0.1.3",
ember-cli-update "0.1.4",
ember-cli-update "0.1.5",
ember-cli-update "0.1.6",
ember-cli-update "0.1.7",
ember-cli-update "0.1.8",
ember-cli-update "0.1.9",
ember-cli-update "0.1.10",
ember-cli-update "0.1.11",
ember-cli-update "0.1.12",
ember-cli-update "0.1.13",
ember-cli-update "0.1.14",
ember-cli-update "0.1.15",
ember-cli-update "0.2.0-beta.1",
ember-cli-update "0.2.0",
ember-cli-update "0.2.1",
ember-cli-update "0.2.2",
ember-cli-update "0.2.3",
ember-cli-update "0.2.4",
ember-cli-update "0.2.5",
ember-cli-update "0.2.6",
ember-cli-update "0.2.7",
ember-cli-update "1.13.0",
ember-cli-update "1.13.1",
ember-cli-update "1.13.5",
ember-cli-update "1.13.6",
ember-cli-update "1.13.7",
ember-cli-update "1.13.8",
ember-cli-update "1.13.9",
ember-cli-update "1.13.10",
ember-cli-update "1.13.11",
ember-cli-update "1.13.12",
ember-cli-update "1.13.13",
ember-cli-update "1.13.14",
ember-cli-update "1.13.15",
ember-cli-update "2.2.0-beta.1",
ember-cli-update "2.2.0-beta.2",
ember-cli-update "2.2.0-beta.3",
ember-cli-update "2.2.0-beta.4",
ember-cli-update "2.2.0-beta.5",
ember-cli-update "2.2.0-beta.6",
ember-cli-update "2.3.0-beta.1",
ember-cli-update "2.3.0-beta.2",
ember-cli-update "2.3.0",
ember-cli-update "2.4.0",
ember-cli-update "2.4.1",
ember-cli-update "2.4.2",
ember-cli-update "2.4.3",
ember-cli-update "2.5.0",
ember-cli-update "2.5.1",
ember-cli-update "2.6.0-beta.1",
ember-cli-update "2.6.0-beta.2",
ember-cli-update "2.6.0-beta.3",
ember-cli-update "2.6.0",
ember-cli-update "2.6.1",
ember-cli-update "2.6.2",
ember-cli-update "2.6.3",
ember-cli-update "2.7.0-beta.1",
ember-cli-update "2.7.0-beta.2",
ember-cli-update "2.7.0-beta.3",
ember-cli-update "2.7.0-beta.4",
ember-cli-update "2.7.0-beta.5",
ember-cli-update "2.7.0-beta.6",
ember-cli-update "2.7.0",
ember-cli-update "2.8.0-beta.1",
ember-cli-update "2.8.0-beta.2",
ember-cli-update "2.8.0-beta.3",
ember-cli-update "2.8.0",
ember-cli-update "2.9.0-beta.1",
ember-cli-update "2.9.0-beta.2",
ember-cli-update "2.9.0",
ember-cli-update "2.9.1",
ember-cli-update "2.10.0-beta.1",
ember-cli-update "2.10.0-beta.2",
ember-cli-update "2.10.0",
ember-cli-update "2.10.1",
ember-cli-update "2.11.0-beta.1",
ember-cli-update "2.11.0-beta.2",
ember-cli-update "2.11.0",
ember-cli-update "2.11.1",
ember-cli-update "2.12.0-beta.1",
ember-cli-update "2.12.0-beta.2",
ember-cli-update "2.12.0",
ember-cli-update "2.12.1",
ember-cli-update "2.12.2",
ember-cli-update "2.12.3",
ember-cli-update "2.13.0-beta.1",
ember-cli-update "2.13.0-beta.2",
ember-cli-update "2.13.0-beta.3",
ember-cli-update "2.13.0-beta.4",
ember-cli-update "2.13.0",
ember-cli-update "2.13.1",
ember-cli-update "2.13.2",
ember-cli-update "2.13.3",
ember-cli-update "2.14.0-beta.1",
ember-cli-update "2.14.0-beta.2",
ember-cli-update "2.14.0",
ember-cli-update "2.14.1",
ember-cli-update "2.14.2",
ember-cli-update "2.15.0-beta.1",
ember-cli-update "2.15.0-beta.2",
ember-cli-update "2.15.0",
ember-cli-update "2.15.1",
ember-cli-update "2.16.0-beta.1",
ember-cli-update "2.16.0-beta.2",
ember-cli-update "2.16.0",
ember-cli-update "2.16.1",
ember-cli-update "2.16.2",
ember-cli-update "2.17.0-beta.1",
ember-cli-update "2.17.0-beta.2",
ember-cli-update "2.17.0",
ember-cli-update "2.17.1",
ember-cli-update "2.17.2",
ember-cli-update "2.18.0-beta.1",
ember-cli-update "2.18.0-beta.2",
ember-cli-update "2.18.0",
ember-cli-update "2.18.1",
ember-cli-update "2.18.2",
ember-cli-update "3.0.0-beta.1",
ember-cli-update "3.0.0-beta.2",
ember-cli-update "3.0.0",
ember-cli-update "3.0.1",
ember-cli-update "3.0.2",
ember-cli-update "3.0.3",
ember-cli-update "3.0.4",
ember-cli-update "3.1.0-beta.1",
ember-cli-update "3.1.0",
ember-cli-update "3.1.1",
ember-cli-update "3.1.2",
ember-cli-update "3.1.3",
ember-cli-update "3.1.4",
ember-cli-update "3.2.0-beta.1",
ember-cli-update "3.2.0-beta.2",
ember-cli-update "3.2.0",
ember-cli-update "3.3.0",
ember-cli-update "3.4.0-beta.1"
ember-cli-update ]
ember-cli-update +441ms
ember-cli-update npm info ember-cli@latest version --json +2ms
ember-cli-update "3.3.0"
ember-cli-update +437ms
git-diff-apply git status --porcelain +0ms
fatal: not a git repository (or any parent up to mount point /)
Stopping at filesystem boundary (GIT_DISCOVERY_ACROSS_FILESYSTEM not set).
Not a git repository
```
I think that it should work independently from used SCM (and even without SCM).

Bắt đầu từ lệnh ember update và theo dõi đầu ra gỡ lỗi của git-diff-apply, đặc biệt là lệnh gọi git status bị lỗi khi ở ngoài một kho lưu trữ Git. Tái hiện lệnh trong một dự án Mercurial hoặc SCM-free; hoàn thành khi quá trình cập nhật kết thúc mà không yêu cầu Git và vẫn giữ nguyên hành vi được yêu cầu.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.