deps: update dependency io.grpc:grpc-bom to v1.31.1 (#16)

Author: renovate-bot

pom.xml

@@ -66,7 +66,7 @@
  <google.common-protos.version>1.17.0</google.common-protos.version>
  <protobuf.version>3.12.4</protobuf.version>
  <junit.version>4.13</junit.version>
- <grpc.version>1.30.0</grpc.version>
+ <grpc.version>1.31.1</grpc.version>
  <guava.version>29.0-android</guava.version>
  </properties>