Bump grpc-protobuf from 1.23.0 to 1.24.0

Bumps [grpc-protobuf](https://github.com/grpc/grpc-java) from 1.23.0 to 1.24.0.
- [Release notes](https://github.com/grpc/grpc-java/releases)
- [Commits](grpc/grpc-java@v1.23.0...v1.24.0)

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

examples/java/build.gradle

@@ -56,7 +56,7 @@ dependencies {
     compile 'com.google.protobuf:protobuf-java:3.9.1'
 
     compile 'io.grpc:grpc-netty:1.23.0'
-    compile 'io.grpc:grpc-protobuf:1.23.0'
+    compile 'io.grpc:grpc-protobuf:1.24.0'
     compile 'com.salesforce.servicelibs:reactor-grpc-stub:0.10.0'
 
     runtime 'ch.qos.logback:logback-classic:1.2.3'