Upgrade to minimum pandas 1.2 and deprecate python 3.5

[gwaybio]

At some point in the future, we should consider making the minimum pandas version >=1.2 in the requirements.txt file.

I debated performing this in #55 because of one silly deprecating in pandas.testing.assert_frame_equal (rtol argument, see 03c09ee). However, I decided that this version upgrade and deprecation should probably be thought through in more detail.

One idea is to mirror the version requirements of pycytominer since both of them are likely going to be used together often. We should also think about certain projects that might no longer be able to use cytominer-eval after this decision, although I think that should be a non-issue since those other projects are probably using a specific cytominer-eval hash.