deps: update protobuf.version to v3.11.4 (#109)

Author: renovate-bot

pom.xml

@@ -157,7 +157,7 @@
  <google.common-protos.version>1.17.0</google.common-protos.version>
  <gax.version>1.53.1</gax.version>
  <grpc.version>1.27.1</grpc.version>
- <protobuf.version>3.11.3</protobuf.version>
+ <protobuf.version>3.11.4</protobuf.version>
  <junit.version>4.13</junit.version>
  <guava.version>28.2-android</guava.version>
  <threeten.version>1.4.1</threeten.version>