Include proxy support

[westlakem]

Our workspace required us to go through proxy authentication to hit an outside server (which is where our code is stored). This PR is what allowed us to use this package through the proxy.

[codecov[bot]]

Codecov Report

Merging #28 into master will decrease coverage by 0.17%. The diff coverage is 75%.

@@            Coverage Diff             @@
##           master      #28      +/-   ##
==========================================
- Coverage   93.51%   93.33%   -0.18%     
==========================================
  Files          14       14              
  Lines         447      450       +3     
  Branches       45       46       +1     
==========================================
+ Hits          418      420       +2     
- Misses         29       30       +1

Impacted Files	Coverage Δ
src/Invoker.ts	89.7% <75%> (-1.07%)	:arrow_down:

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