deps: update dependency com.google.protobuf:protobuf-bom to v3.11.4 (#77)

Author: renovate-bot

pom.xml

@@ -68,7 +68,7 @@
     <google.common-protos.version>1.17.0</google.common-protos.version>
     <gax.version>1.53.1</gax.version>
     <grpc.version>1.27.0</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>