Upgrade to protobuf plugin 0.3.1
The plugin has been published on plugins.gradle.org
Conforming to the Gradle standard that plugin IDs must be name-spaced,
the plugin ID has been changed to com.google.protobuf.
diff --git a/compiler/build.gradle b/compiler/build.gradle
index b0d9113..6f67a3d 100644
--- a/compiler/build.gradle
+++ b/compiler/build.gradle
@@ -1,5 +1,5 @@
apply plugin: "cpp"
-apply plugin: "protobuf"
+apply plugin: "com.google.protobuf"
description = 'The protoc plugin for gRPC Java'