.circleci: Bump python3.7 -> python3.8

[seemethere]

Adds python 3.8 to the matrix.

Related PRs:

• .circleci: Add workflows for Python 3.8 pytorch#31948
• .circleci: Bump python3.7 -> python3.8 audio#397

[fmassa]

Hi Eli,

Thanks for the PR!

The test failures that you are seeing are unrelated and have been fixed in master, can you rebase your PR?

[codecov-io]

Codecov Report

Merging #1731 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master   #1731   +/-   ##
======================================
  Coverage    0.43%   0.43%           
======================================
  Files          92      92           
  Lines        7386    7386           
  Branches     1111    1111           
======================================
  Hits           32      32           
  Misses       7346    7346           
  Partials        8       8

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[fmassa]

LGTM in general, but Python 3.8 CI is not working yet.

[bottler]

I think mac and windows are failing because torch isn't yet working for them on python 3.8.

One problem for the linux conda builds is the dependency on typing, which is only relevant for python 3.5 and earlier, but depending on it for python 3.6 and 3.7 is somehow tolerated by conda.
There's a line

typing -> python[version='2.7.*|3.4.*|3.5.*|3.6.*|>=2.7,<2.8.0a0|>=3.5,<3.6.0a0|>=3.6,<3.7.0a0|>=3.7,<3.8.0a0']

in the output of one of the failed builds.

I plan to make a separate PR soon which makes typing only get included when necessary, unless someone suggests otherwise.

[seemethere]

Just did a rebase off of master with @bottler's changes, should hopefully resolve all of the issues.

EDIT: Actually needed to run a nightly run of upstream pytorch/pytorch after we merged in my changes to add python 3.8 to the nightly pipeline.