bump python version

[katiebreivik]

github pages break with fixed 3.7 version

[codecov[bot]]

Codecov Report

Merging #564 (8eee916) into develop (a234366) will increase coverage by 0.00%. The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop     #564   +/-   ##
========================================
  Coverage    87.12%   87.13%           
========================================
  Files           40       40           
  Lines        25373    25392   +19     
========================================
+ Hits         22106    22123   +17     
- Misses        3267     3269    +2     

Impacted Files	Coverage Δ
cosmic/sample/initialcmctable.py	95.49% <0.00%> (+0.14%)	:arrow_up:
cosmic/sample/initialbinarytable.py	94.44% <0.00%> (+0.16%)	:arrow_up:
cosmic/sample/sampler/independent.py	64.84% <0.00%> (+0.87%)	:arrow_up:

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[katiebreivik]

Super simple update to the website deploy action.