* master: (26 commits)
  Functions Interop (#2113)
  Add a travis cron job for CocoaPod symbol collision testing (#2154)
  Save schema version on downgrade, add test to verify (#2153)
  Silence Storage Unit Test `nil` warning. (#2150)
  Update versions for Release 5.14.0 (#2145)
  gRPC: fix cases where gRPC call could be finished twice (#2146)
  Fix Swizzler test warnings (#2144)
  Update Auth CHANGELOG.md (#2128)
  Make fuzz tests optional until they pass (#2143)
  Add support of Game Center sign in (#2127)
  Add test for deprecated FDLURLComponents init API. (#2133)
  fix a typo in integration test (#2131)
  Make fuzzing less verbose to avoid exceeding Travis log limit (#2126)
  Move to `domainURIPrefix` for FIRDynamicLinkComponents (#2119)
  Carthage instructions for new gRPCCertificates.bundle location (#2132)
  Fix pod lib lint GoogleUtilities.podspec --use-libraries regression (#2130)
  Avoid using default FIROptions directly. (#2124)
  Changelog entry for LRU GC (#2122)
  Revert "Add Firebase Source to Header Search Path" (#2123)
  Custom fdl domain (#2121)
  ...