Merge pull request #1557 from nextcloud/androidGradle300beta6

update to gradle:3.0.0-beta6

build.gradle

@@ -14,7 +14,7 @@ buildscript {
         google()
     }
     dependencies {
-        classpath 'com.android.tools.build:gradle:3.0.0-beta5'
+        classpath 'com.android.tools.build:gradle:3.0.0-beta6'
         classpath 'com.google.gms:google-services:3.0.0'
     }
 }