updating gradle-plugin to 3.0.0-beta7 including foced move to buildToolsVersion 26.0.2

build.gradle

@@ -14,7 +14,7 @@ buildscript {
         google()
     }
     dependencies {
-        classpath 'com.android.tools.build:gradle:3.0.0-beta6'
+        classpath 'com.android.tools.build:gradle:3.0.0-beta7'
         classpath 'com.google.gms:google-services:3.0.0'
     }
 }
@@ -65,7 +65,7 @@ android {
     }
 
     compileSdkVersion 25
-    buildToolsVersion '25.0.2'
+    buildToolsVersion '26.0.2'
 
     defaultConfig {
         testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"