error when generate diff files. sketch 46
### How did it happen?
1. error when generate diff files. sketch 46
2.
3.


### Error log

```
Traceback (most recent call last):
  File "/Users/lmz/Library/Application Support/com.bohemiancoding.sketch3/Plugins/Git.sketchplugin/getArtboardNames.py", line 15, in <module>
    name = pageName + "/" + artboardName
TypeError: can't concat bytes to str

```