upgrade gradle version to be compatible with openjdk14.0.1

Author: fishercoder1534

gradle/wrapper/gradle-wrapper.jar

@@ -1,6 +1,5 @@
-#Sat Aug 10 07:31:35 PDT 2019
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-4.8.1-bin.zip
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-4.4-all.zip