Upgraded gradle to cope with java9

Author: hierynomus

.travis.yml

@@ -4,9 +4,10 @@ sudo: required
 
 services:
   - docker
-  
+
 before_cache:
   - rm -f $HOME/.gradle/caches/modules-2/modules-2.lock
+  - rm -fr $HOME/.gradle/caches/*/plugin-resolution/
 
 cache:
   directories:

gradle/wrapper/gradle-wrapper.properties

@@ -3,4 +3,4 @@ distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-4.0-all.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-4.3-all.zip