Test if has any conflicts with matplotlib and basemap

[seisman]

Fixes #66

[leouieda]

@seisman thanks for this! I think the failure is because the install is mixing packages from the default and conda-forge channels. Matplotlib is already being installed because we use it for testing. The easiest solution is to just add basemap to the requirements.txt file instead of creating a separate build just for this.

[seisman]

Didn't know that there are some incompatibility between the default channel and conda-forge channel.
I'll close this PR and open a new one.

[leouieda]

Yeah, that's one of the tricky parts about using conda and the reason why I included the conda env part in the install instructions. See https://conda-forge.org/docs/conda-forge_gotchas.html#using-multiple-channels