Pin all production dependencies

[brettcannon]

Fixes #1374

This pull request:

• Has a title summarizes what is changing
• Includes a news entry file (remember to thank yourself!)
• Has unit tests & code coverage is not adversely affected (within reason)
• Works on all actively maintained versions of Python (e.g. Python 2.7 & the latest Python 3 release)
• Works on Windows 10, macOS, and Linux (e.g. considered file system case-sensitivity)

[codecov]

Codecov Report

Merging #1375 into master will decrease coverage by 0.36%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1375      +/-   ##
==========================================
- Coverage   71.45%   71.08%   -0.37%     
==========================================
  Files         269      269              
  Lines       12403    12403              
  Branches     2199     2199              
==========================================
- Hits         8862     8817      -45     
- Misses       3411     3450      +39     
- Partials      130      136       +6

Impacted Files	Coverage Δ
src/client/linters/errorHandlers/notInstalled.ts	33.33% <0%> (-61.12%)	⬇️
src/client/linters/errorHandlers/errorHandler.ts	77.77% <0%> (-22.23%)	⬇️
src/client/common/logger.ts	53.33% <0%> (-20.01%)	⬇️
src/client/common/application/applicationShell.ts	23.07% <0%> (-7.7%)	⬇️
src/client/debugger/PythonProcess.ts	45.83% <0%> (-5.42%)	⬇️
src/client/common/installer/productInstaller.ts	60.31% <0%> (-4.24%)	⬇️
src/client/linters/baseLinter.ts	87.5% <0%> (-4.17%)	⬇️
...reter/locators/services/cacheableLocatorService.ts	91.83% <0%> (-4.09%)	⬇️

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