`nim c` can't resolve packages when NIMBLE_DIR env var is set
I think this might be a problem with Nim, not nimble per se, but I wasn't sure so I'm filing an issue here first.

Using Nim `#version-2-0` installed via choosenim, if I have `NIMBLE_DIR` set in my shell environment, `nim c` is unable to locate installed packages in `${NIMBLE_DIR}/pkgs2/`. In my shell, if I `unset NIMBLE_DIR` then `nim c` works correctly.

With previous versions of nim/nimble, `nim c` finds the installed packages in `${NIMBLE_DIR}/pkgs/` no problem.