update gradle wrapper to latest version to work with Java 10

Author: tschie

build.gradle

@@ -51,5 +51,5 @@ run {
 }
 
 task wrapper(type: Wrapper) {
-    gradleVersion = '4.3.1'
+    gradleVersion = '4.8'
 }

gradle/wrapper/gradle-wrapper.jar

@@ -1,5 +1,5 @@
-distributionUrl=https\://services.gradle.org/distributions/gradle-4.3.1-bin.zip
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-zipStorePath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-4.8-bin.zip
 zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists