chore: add node 11 ci job

[mayurkale22]

I am optimistic about tests and build, Let's see how much work required to add support for node 11.

[codecov-io]

Codecov Report

Merging #375 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #375   +/-   ##
=======================================
  Coverage   95.19%   95.19%           
=======================================
  Files         128      128           
  Lines        8492     8492           
  Branches      628      628           
=======================================
  Hits         8084     8084           
  Misses        408      408

Impacted Files	Coverage Δ
test/test-grpc.ts	99.68% <0%> (ø)	⬆️
src/grpc.ts	93.69% <0%> (ø)	⬆️
src/grpc-stats/server-stats.ts
src/grpc-stats/client-stats.ts
src/grpc-stats/server-metrics.ts	100% <0%> (ø)
src/grpc-stats/client-metrics.ts	100% <0%> (ø)

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[mayurkale22]

@draffensperger Looks like node 11 is good to go. Should we include in the ci job?

[draffensperger]

Yes, sounds good!