Upgrade REST Assured sample to build with Gradle 4.3

See gh-446

Author: wilkinsona

samples/rest-assured/gradle/wrapper/gradle-wrapper.jar

@@ -1,6 +1,6 @@
-#Thu Mar 23 11:48:10 GMT 2017
+#Mon Nov 06 21:06:01 GMT 2017
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-3.4.1-bin.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-4.3-bin.zip