Upgrades typescript to 3.9.5

[cloudify]

Gets rid of the following warning:

warning "durable-functions > typedoc@0.17.7" has incorrect peer dependency "typescript@>=3.8.3".

[codecov-commenter]

Codecov Report

Merging #91 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #91   +/-   ##
=======================================
  Coverage   84.18%   84.18%           
=======================================
  Files          26       26           
  Lines         759      759           
  Branches       74       74           
=======================================
  Hits          639      639           
  Misses        116      116           
  Partials        4        4           

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