Bump grpc-protobuf from 1.15.1 to 1.22.1

Bumps [grpc-protobuf](https://github.com/grpc/grpc-java) from 1.15.1 to 1.22.1.
- [Release notes](https://github.com/grpc/grpc-java/releases)
- [Commits](grpc/grpc-java@v1.15.1...v1.22.1)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

examples/java/build.gradle

@@ -56,7 +56,7 @@ dependencies {
     compile 'com.google.protobuf:protobuf-java:3.9.0'
 
     compile 'io.grpc:grpc-netty:1.22.1'
-    compile 'io.grpc:grpc-protobuf:1.15.1'
+    compile 'io.grpc:grpc-protobuf:1.22.1'
     compile 'com.salesforce.servicelibs:reactor-grpc-stub:0.10.0'
 
     runtime 'ch.qos.logback:logback-classic:1.2.3'