Bug 1220633 - Gradle wrapper: Use distribution with sources. r=trivial

This will enable Gradle API/DSL documentation in IntelliJ.

--HG--
extra : commitid : ajftBsY437

gradle/wrapper/gradle-wrapper.properties

-#Sun Oct 18 17:00:46 PDT 2015
+#Mon Nov 02 13:44:39 GMT 2015
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-2.7-bin.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-2.7-all.zip