Plugin won't work if not in the root of git repository

```
$ git describe
1.2.3-1-gc18d12c
```
When executed from subdirectory I expect
```
$ ./gradlew cV -q
Project version: 1.2.3-SNAPSHOT
```

But actually I get
```
$ ./gradlew cV -s

> Configure project :
Failed to open repository, trying to work without it org.eclipse.jgit.errors.RepositoryNotFoundException: repository not found: ********
Could not resolve current position on uninitialized repository, returning default
Couldn't perform check uncommitted changes command on uninitialized repository

> Task :currentVersion

Project version: 0.1.0-SNAPSHOT
```

Plugin version: 1.9.1

Tested environments environments
```
JVM: 1.8.0_171 (Oracle Corporation 25.171-b11)
OS: Mac OS X 10.13.4 x86_64
```
```
JVM: 1.8.0_171 (Oracle Corporation 25.171-b10)
OS: Linux 3.10.0-862.3.2.el7.x86_64 amd64
```