COMP: Fix appveyor package upload by using "Python38-x64" instead of "Python27-x64"

[jcfr]

This commit attempts to address the following errors:

pip : DEPRECATION: Python 2.7 will reach the end of its life on January 1st, 2020. Please upgrade your Python as Python 2.7 won't be maintained after that date. A future version of pip will drop support for Python 2.7. More
details about Python 2 support in pip, can be found at https://pip.pypa.io/en/latest/development/release-process/#python-2-support
At line:1 char:1
+ pip install scikit-ci-addons==0.18.0
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (DEPRECATION: Py...ython-2-support:String) [], RemoteException
    + FullyQualifiedErrorId : NativeCommandError

[...]

ERROR: Could not find a version that satisfies the requirement backoff~=2.1.2 (from githubrelease>=1.5.6->scikit-ci-addons==0.18.0) (from versions: 1.0, 1.0.1, 1.0.2, 1.0.3, 1.0.4, 1.0.5, 1.0.6, 1.0.7, 1.1.0, 1.2.0, 1.2.1,
1.3.0, 1.3.1, 1.3.2, 1.4.0, 1.4.1, 1.4.2, 1.4.3, 1.5.0, 1.6.0, 1.7.0, 1.7.1, 1.8.0, 1.8.1, 1.9.0, 1.9.1, 1.9.2, 1.10.0, 1.11.0, 1.11.1)
ERROR: No matching distribution found for backoff~=2.1.2 (from githubrelease>=1.5.6->scikit-ci-addons==0.18.0)

[jamesobutler]

COMP: Fix appveyor package upload using "Python38-x64" instead of "Python27-x64" ->
COMP: Fix appveyor package upload using "Python27-x64" instead of "Python38-x64"?

[jcfr]

Thanks for the review 🙏

It turns out we are effectively switching the python env. used to run scikit-ci-addons from 2.7 to 3.8. Considering this, I think the pull request title is correct.

[jamesobutler]

Ah I understand now. Fix appveyor package upload using "Python38-x64" sounded like the broken package upload was using "Python38-x64". Instead it is describing how it is being fixed not what was wrong. No need to update the commit title, but might've been clearer as:
COMP: Fix appveyor package upload using "Python38-x64" instead of "Python27-x64" ->
COMP: Fix appveyor package upload by using "Python38-x64" instead of "Python27-x64

[jcfr]

While the commit as already been integrated, for future reference, I updated the pull request title.