deps: update dependency com.google.protobuf:protobuf-java to v3.11.1 (#18)

Author: renovate-bot

pom.xml

@@ -68,7 +68,7 @@
     <google.common-protos.version>1.17.0</google.common-protos.version>
     <gax.version>1.51.0</gax.version>
     <grpc.version>1.25.0</grpc.version>
-    <protobuf.version>3.10.0</protobuf.version>
+    <protobuf.version>3.11.1</protobuf.version>
     <junit.version>4.12</junit.version>
     <guava.version>28.1-android</guava.version>
     <threeten.version>1.4.0</threeten.version>