[Snyk] Security upgrade python from 3.7-alpine to 3.9-alpine

[snyk-bot]

Keeping your Docker base image up-to-date means you’ll benefit from security fixes in the latest version of your chosen image.

Changes included in this PR

• Dockerfile

We recommend upgrading to python:3.9-alpine, as this image has only 0 known vulnerabilities. To do this, merge this pull request, then verify your application still works as expected.

Some of the most important vulnerabilities in your base image include:

Severity	Priority Score / 1000	Issue	Exploit Maturity
	571	Integer Overflow or Wraparound SNYK-ALPINE315-EXPAT-2342160	No Known Exploit
	471	Integer Overflow or Wraparound SNYK-ALPINE315-EXPAT-2342162	No Known Exploit
	471	Integer Overflow or Wraparound SNYK-ALPINE315-EXPAT-2342163	No Known Exploit
	571	Integer Overflow or Wraparound SNYK-ALPINE315-EXPAT-2342164	No Known Exploit
	571	Integer Overflow or Wraparound SNYK-ALPINE315-EXPAT-2342165	No Known Exploit

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[codecov]

Codecov Report

Merging #69 (88b38a8) into master (08f62ec) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #69   +/-   ##
=======================================
  Coverage   86.04%   86.04%           
=======================================
  Files           3        3           
  Lines         387      387           
  Branches       91       91           
=======================================
  Hits          333      333           
  Misses         46       46           
  Partials        8        8           

[coveralls]

Coverage remained the same at 87.339% when pulling 88b38a8 on snyk-fix-1621c0d6a78bcebb0cb33e331d511e9d into 08f62ec on master.