Exporter/jaeger: Enforce strictNullChecks and noUnusedLocals

[mayurkale22]

This is part of #348

[codecov-io]

Codecov Report

Merging #382 into master will decrease coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #382      +/-   ##
==========================================
- Coverage   94.81%   94.77%   -0.04%     
==========================================
  Files         136      136              
  Lines        8941     8942       +1     
  Branches      648      650       +2     
==========================================
- Hits         8477     8475       -2     
- Misses        464      467       +3

Impacted Files	Coverage Δ
src/stackdriver-monitoring.ts	81.05% <0%> (-3.16%)	⬇️
src/jaeger-driver/index.ts	97.22% <0%> (-0.08%)	⬇️
test/test-jaeger.ts	99.21% <0%> (ø)	⬆️
src/jaeger.ts	83.51% <0%> (+0.37%)	⬆️

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[draffensperger]

Nice!