taskbookDirectory with utf-8 not working

**Describe the bug**
When setting taskbookDirectory to a path with a utf-8 character like é I get the following error message:
✖ Custom app directory was not found on your system: /Users/user/Test�/taskbook

**To Reproduce**
Set taskbookDirectory to a path containing utf-8 character

**Expected behavior**
taskbookDirectory should work with utf-8 characters

**Technical Info (please complete the following information)**
- OS: MacOS Mojave 10.14.2
- Node.js Version: v11.8.0
- Taskbook Version: 0.2.0

Thanks

Start by locating the code that reads or validates taskbookDirectory and reproduce the issue with a path containing é on macOS. Trace where the path becomes corrupted, then verify that taskbookDirectory accepts UTF-8 paths and no longer reports a false missing-directory error.

Written by the indexing model from the issue text.