chore(deps): update gax.version to v1.50.0 (googleapis#18)

Author: renovate-bot

pom.xml

@@ -67,7 +67,7 @@
  <google.core.version>1.91.3</google.core.version>
  <google.api-common.version>1.8.1</google.api-common.version>
  <google.common-protos.version>1.17.0</google.common-protos.version>
- <gax.version>1.49.1</gax.version>
+ <gax.version>1.50.0</gax.version>
  <grpc.version>1.25.0</grpc.version>
  <protobuf.version>3.10.0</protobuf.version>
  <junit.version>4.12</junit.version>