[TST] conditionally skip 3.8 tests needing quilt

[sjsrey]

It looks like quilt is not available for 3.8 on conda-forge:

So, I think that is why the ci couldn't solve for the testing env.

This PR starts some conditional skipping if quilt isn't available.

Looks to be working

To do

• add warnings that quilt isn't available
• update docs

[codecov-commenter]

Codecov Report

Merging #78 into master will increase coverage by 0.31%.
The diff coverage is 95.23%.

@@            Coverage Diff             @@
##           master      #78      +/-   ##
==========================================
+ Coverage   77.27%   77.59%   +0.31%     
==========================================
  Files          11       11              
  Lines         528      540      +12     
==========================================
+ Hits          408      419      +11     
- Misses        120      121       +1     

Impacted Files	Coverage Δ
tobler/tests/test_interpolators.py	97.82% <95.23%> (-2.18%)	⬇️

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[knaaptime]

cool, thanks for this. I think is an issue with one of quilt's dependencies not being on conda (you can pip install quilt in a 3.8 env), and its really difficult to tell which.

[sjsrey]

The way this is set up (I think) once they do release quilt on conda for 3.8, the tests will get run. Before then only the 3.6 and 3.7 tests will run (which pass).
What I was hoping to do is get a release of Tobler that doesn't block a 3.8 conda install of the meta package, and I think this would do it?

[knaaptime]

looks good to me