Use stable version of rustfmt/clippy

We currently use ruftfmt and clippy with a toolchain nightly-2019-05-17.
But the stable version have caught up to our last nightly version.

nightly nightly-05-17:
rustfmt 1.2.2-nightly (5274b49 2019-04-24)
clippy 0.0.212 (ad3269c 2019-05-14)

stable 1.36:
rustfmt 1.2.2-stable (5274b49 2019-04-24)
clippy 0.0.212 (082cfa7 2019-06-07)

We might update our nightly toolchain version, or just stick with the stable version.
I think the latter is better. It works well with the existing ecosystem (eg. IntelliJ) and requires less attention to keep up with recent version.

issue 中沒有指定檔案或測試。找到選擇 nightly-2019-05-17 的設定以及呼叫 rustfmt 和 clippy 的檢查，然後驗證穩定版 1.36 toolchain 能夠通過專案現有的檢查。完成的標準是專案使用穩定版 toolchain，且這些檢查沒有回歸問題。

由索引模型根據 Issue 內容生成。