Fix: createScopedRequired depcreated in google-auth-library 3.0.0

[mayurkale22]

Fixes #429

DeprecationWarning: The createScopedRequired method on the JWT class has been deprecated, and will be removed in the 3.0 release of google-auth-library.

These changes have all been tested locally and been confirmed to be working.

[mayurkale22]

/cc @diiiego83

[codecov-io]

Codecov Report

Merging #467 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #467      +/-   ##
==========================================
- Coverage   94.66%   94.65%   -0.01%     
==========================================
  Files         150      150              
  Lines        9705     9657      -48     
  Branches      734      717      -17     
==========================================
- Hits         9187     9141      -46     
+ Misses        518      516       -2

Impacted Files	Coverage Δ
test/test-tracecontext-format.ts	95.45% <0%> (-3.62%)	⬇️
src/stackdriver-monitoring.ts	78.65% <0%> (-1.56%)	⬇️
src/tracecontext-format.ts	95% <0%> (-1.43%)	⬇️
src/binary-format.ts	100% <0%> (ø)	⬆️
test/test-prometheus-stats.ts	100% <0%> (ø)	⬆️
src/validators.ts	100% <0%> (ø)	⬆️
src/stackdriver-cloudtrace.ts	93.33% <0%> (+0.79%)	⬆️

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[draffensperger]

Are these code paths already covered by tests? If not, would it make sense to add any new ones?

[jinmel]

what is blocking this from merge?

[mayurkale22]

Are these code paths already covered by tests? If not, would it make sense to add any new ones?

Yes this is already covered by tests.