Polish "Add Grails sample app" (1338df9)

The sole structural change is to rearrange the build slightly so that,
like the other samples, the version of the Grails sample's REST Docs
dependency is automatically updated.

See gh-250

samples/rest-notes-grails/grails-app/controllers/com/example/InternalServerErrorController.groovy

@@ -1,11 +1,28 @@
+/*
+ * Copyright 2014-2016 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
 package com.example
 
 class InternalServerErrorController {
 
-    def index() {
-        render(contentType: 'application/json') {
-            error = 500
-            message = "Internal server error"
-        }
-    }
+	def index() {
+		render(contentType: 'application/json') {
+			error = 500
+			message = "Internal server error"
+		}
+	}
+
 }