[works the 2nd time] File doesn't exist: utf8proc_data.c
for reference: https://gitter.im/nimgen/Lobby?at=5bf5dfa087c4b86bccf7de41

```
nimble install 'http://github.com/genotrance/nimtreesitter?subdir=treesitter'
Downloading http://github.com/genotrance/nimtreesitter using git (subdir is 'treesitter')
Setting up Git repo
Checking out artifacts
Resetting Git repo
File doesn't exist: utf8proc_data.c
stack trace: (most recent call last)
/private/tmp/nimble_87594/githubcom_genotrancenimtreesitter/treesitter/treesitter.nimble(28) installBefore
/private/tmp/nimble_87594/githubcom_genotrancenimtreesitter/treesitter/treesitter.nimble(25) setupTask
/Users/timothee/git_clone/nim/Nim/lib/system/nimscript.nim(237) exec
/Users/timothee/git_clone/nim/Nim/lib/system/nimscript.nim(237, 7) Error: unhandled exception: FAILED: nimgen treesitter.cfg
```

note: 2nd time, it seemed to work; not sure what it failed 1st time
