Generate pretty diffs error
### How did it happen?
1. Try to generate pretty diffs and bad things happens..
2.
3.


### Error log

```
mv: rename .exportedArtboards/Reach MVP to .oldArtboards: No such file or directory
/Users/admin/Library/Application Support/com.bohemiancoding.sketch3/Plugins/Git.sketchplugin//exportArtboard.sh: line 36: ${readmeFile}: ambiguous redirect

```