Switch back from git-based to release-based GeoUtils in dev-environment

[rhugonnet]

To avoid having to put a release out every time we change something in GeoUtils in order for the tests to pass, I switched the dev-environment.yml source for GeoUtils from conda:

- geoutils

to the latest git version:

- pip:
  - git+https://github.com/GlacioHack/GeoUtils.git

This was done in #265.

We should switch back to release-based GeoUtils once both packages have reached a minimal level of maturity and documentation (e.g., version 0.1 ?).