Update protoc dependency version in template

templates/src/objective-c/!ProtoCompiler-gRPCPlugin.podspec.template

@@ -103,7 +103,7 @@
     s.preserve_paths = plugin
 
     # Restrict the protoc version to the one supported by this plugin.
-    s.dependency '!ProtoCompiler', '3.0.2'
+    s.dependency '!ProtoCompiler', '3.1.0'
     # For the Protobuf dependency not to complain:
     s.ios.deployment_target = '7.1'
     s.osx.deployment_target = '10.9'