Add test to reproduce the error caused by (no branch).
Fix test: return error when the current branch check out to a commit.
Merge pull request #33 from shaoshing/no-branch

Fix error when getting the current branch but it is checked out to a commit
Bumped version to 0.4.3
Use svg instead of png to get better image quality
Merge pull request #40 from PeterDaveHello/patch-2

Use svg instead of png to get better image quality
Use spawn instead of exec
Read file contents as UTF-8 instead of buffer