Upgrade Gradle to version 4.8

https://docs.gradle.org/4.8/release-notes.html

Author: swegner

gradle/wrapper/gradle-wrapper.jar

@@ -17,6 +17,6 @@
 ################################################################################
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-4.8-bin.zip
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-4.7-bin.zip