bug: Handle FCM client not available

[jrconlin]

• update twisted library

Closes #1348

[codecov-io]

Codecov Report

Merging #1349 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1349      +/-   ##
==========================================
+ Coverage   99.74%   99.74%   +<.01%     
==========================================
  Files          64       64              
  Lines       10433    10449      +16     
==========================================
+ Hits        10406    10422      +16     
  Misses         27       27

Impacted Files	Coverage Δ
autopush/tests/test_router.py	99.89% <100%> (ø)	⬆️
autopush/router/fcmv1client.py	100% <100%> (ø)	⬆️
autopush/router/fcm_v1.py	100% <100%> (ø)	⬆️

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