Cannot build project in git repo without HEAD
Seems like newest nimble doesn't work for me.

How to reproduce:
```
> nimble --version
nimble v0.13.1 compiled at 2021-09-26 00:55:29
git hash: couldn't determine git hash
> nimble init test
...(press Enter for everything)...
> cd test
> nimble build
  Verifying dependencies for test@0.1.0
   Warning: Not removing temporary path because of debug verbosity: /tmp/nimble_40149
tables.nim(234)          raiseKeyError
Error: unhandled exception: key not found: url [KeyError]
```