Update Gradle wrapper to 4.6

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1833292 13f79535-47bb-0310-9956-ffa450edef68

build.gradle

@@ -45,7 +45,7 @@ allprojects {
     apply plugin: 'eclipse'
 
     task wrapper(type: Wrapper) {
-        gradleVersion = '3.4.1'
+        gradleVersion = '4.6'
     }
 
     task adjustWrapperPropertiesFile {

gradle/wrapper/gradle-wrapper.properties

@@ -1,5 +1,5 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-3.4.1-bin.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-4.6-bin.zip
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists