Upgrade Gradle wrapper to 5.2.1

gradlew

@@ -4,20 +4,6 @@
 ##
 ##  Gradle start up script for UN*X
 ##
-##  Copyright 2017 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.
-##
 ##############################################################################
 
 # Attempt to set APP_HOME