Revert "CI: Pin miniconda version"

[TomAugspurger]

https://ci.appveyor.com/project/pandas-dev/pandas/build/1.0.5024/job/vpdwnlx9je8a4sfw#L1273

https://travis-ci.org/pandas-dev/pandas/jobs/280513252#L1377

We want to revert #17700 pinning miniconda

We want to keep

• 7bc883e
• a33d078

The bzip2 conda package that started this has been fixed by a new build.

The only remaining issue should be the gcc that's picked up on linux. I'll keep an eye on conda/conda#6030

[TomAugspurger]

This warning is strange. Shouldn't that be an exception?

[jreback]

why would these be showing up now?

[TomAugspurger]

No idea. A new anaconda distribution was released today, which shouldn't directly affect us, but maybe a package update? I'm asking around internally to see if anyone knows what's up.

[jreback]

this is not an issue with bzip2
rather i think it's a new version of pytables

we have a default which i think just changed

[jorisvandenbossche]

A new anaconda distribution was released today

I see in the changelog of Anaconda 5 that libgccy has been removed (which may be related)