Update uncompressedSize and compressedSize for the exporters

[mayurkale22]

This PR is based on the discussion here: census-instrumentation/opencensus-website#580.

[codecov-io]

Codecov Report

Merging #347 into master will increase coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #347      +/-   ##
==========================================
+ Coverage   95.14%   95.15%   +<.01%     
==========================================
  Files         122      122              
  Lines        8474     8478       +4     
  Branches      750      754       +4     
==========================================
+ Hits         8063     8067       +4     
  Misses        411      411

Impacted Files	Coverage Δ
test/test-ocagent.ts	91.74% <0%> (ø)	⬆️
test/test-stackdriver-cloudtrace-utils.ts	100% <0%> (ø)	⬆️
src/adapters.ts	97% <0%> (+0.06%)	⬆️
src/stackdriver-cloudtrace-utils.ts	97.26% <0%> (+0.07%)	⬆️

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[draffensperger]

Thanks for doing this!