conda recipe should use matplotlib-base

[jamesmyatt]

According to the conda-forge docs, the conda recipe should probably depend on the matplotlib-base package, rather than matplotlib: https://conda-forge.org/docs/maintainer/knowledge_base.html#matplotlib

Is this right? Does captum require pyqt as well or just matplotlib?

For example: conda-forge/geoplot-feedstock#19

[vivekmig]

Thanks @jamesmyatt , this is a great catch! Captum only requires matplotlib but not pyqt, we will update the recipe to depend on matplotlib-base instead.