Changed the GitClient for commit in branch retrieval

Changes to be committed:
	modified:   git-client/src/main/java/nl/tudelft/ewi/git/client/Repositories.java
	modified:   git-client/src/main/java/nl/tudelft/ewi/git/client/RepositoriesImpl.java
	modified:   git-client/src/test/java/nl/tudelft/ewi/git/client/RepositoriesMock.java