Update dependency grpc to ~1.20.0

[renovate]

This PR contains the following updates:

Package	Type	Update	Change	References
grpc	dependencies	minor	~1.19.0 -> ~1.20.0	homepage, source

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Release Notes

grpc/grpc-node

v1.20.2

Compare Source

v1.20.0

Compare Source

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[codecov-io]

Codecov Report

Merging #489 into master will decrease coverage by 0.05%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #489      +/-   ##
==========================================
- Coverage   95.01%   94.95%   -0.06%     
==========================================
  Files         143      142       -1     
  Lines        9299     9192     -107     
  Branches      515      516       +1     
==========================================
- Hits         8835     8728     -107     
  Misses        464      464

Impacted Files	Coverage Δ
src/http-stats.ts	100% <0%> (ø)	⬆️
src/grpc-stats/server-stats.ts	100% <0%> (ø)	⬆️
src/grpc-stats/client-stats.ts	100% <0%> (ø)	⬆️
test/test-prometheus-stats.ts	100% <0%> (ø)	⬆️
src/grpc-stats/stats-common.ts	100% <0%> (ø)	⬆️
src/grpc-stats/common-distributions.ts

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