Add Python 3.8 as supported

[gliptak]

#945

Thank you for the ping @jpangburn

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-io]

Codecov Report

Merging #1256 into master will increase coverage by 0.05%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1256      +/-   ##
==========================================
+ Coverage   94.43%   94.49%   +0.05%     
==========================================
  Files          71       71              
  Lines        3630     3669      +39     
  Branches      717      717              
==========================================
+ Hits         3428     3467      +39     
  Misses        103      103              
  Partials       99       99

Impacted Files	Coverage Δ
samtranslator/model/naming.py	100% <0%> (ø)	⬆️
...amtranslator/policy_template_processor/template.py	100% <0%> (ø)	⬆️
...mtranslator/policy_template_processor/processor.py	100% <0%> (ø)	⬆️
...nslator/model/preferences/deployment_preference.py	100% <0%> (ø)	⬆️
samtranslator/sdk/resource.py	100% <0%> (ø)	⬆️
samtranslator/model/exceptions.py	100% <0%> (ø)	⬆️
samtranslator/region_configuration.py	100% <0%> (ø)	⬆️
samtranslator/intrinsics/actions.py	98.71% <0%> (ø)	⬆️
samtranslator/plugins/globals/globals.py	99.05% <0%> (+0.02%)	⬆️
samtranslator/model/__init__.py	98.14% <0%> (+0.03%)	⬆️
... and 6 more

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[gliptak]

@ShreyaGangishetty the PR is green

[ShreyaGangishetty]

@gliptak Thank you for contributing this!
This PR looks good to me