Update health.proto to add objc prefix (#166)

* Update health.proto to add objc prefix

* Use GRPCV1 instead of GRPC for objc prefix

* Update objc prefix to GrpcHealthV1

Author: charlottetan

grpc/health/v1/health.proto

@@ -24,6 +24,7 @@ option go_package = "google.golang.org/grpc/health/grpc_health_v1";
 option java_multiple_files = true;
 option java_outer_classname = "HealthProto";
 option java_package = "io.grpc.health.v1";
+option objc_class_prefix = "GrpcHealthV1";
 
 message HealthCheckRequest {
   string service = 1;