Build tools: Set astropy minimum requirement to 1.2 to help the CIs.

[hmaarrfk]

Description

Not too sure astropy was ever installed successfully.

Checklist

• Docstrings for all functions
• Gallery example in ./doc/examples (new features only)
• Benchmark in ./benchmarks, if your changes aren't covered by an
  existing benchmark
• Unit tests
• Clean style in the spirit of PEP8

For reviewers

• Check that the PR title is short, concise, and will make sense 1 year
  later.
• Check that new functions are imported in corresponding __init__.py.
• Check that new features, API changes, and deprecations are mentioned in
  doc/release/release_dev.rst.
• Consider backporting the PR with @meeseeksdev backport to v0.14.x

[hmaarrfk]

@scikit-image/core fun fun, the pip quiet flag also fails silently ;) seems like astropy upgraded. We need to find an "older version" of astropy that we want to include in our minimum requirements pinnings.

https://travis-ci.org/scikit-image/scikit-image/jobs/497867990#L2071

[stefanv]

Feel free to pick one and move on. I think we only use this to test our fits plugin.

[hmaarrfk]

I was able to use astropy 1.0 to import pyfits. astropy 0.4 didn't install on my system (being very descriptive here).

Astropy 1.2 has wheels python 2.7 and 3.5, so I think that is the best thing to do for our CIs and backport.

Astropy 1.3 has wheels for 3.6 too.

[hmaarrfk]

@meeseeksdev backport to v0.14.x

[lumberbot-app]

Something went wrong ... Please have a look at my logs.