Revert "downgrade build tools version"

This reverts commit 82492de4ee.

android/app/build.gradle

@@ -3,7 +3,7 @@ apply from: '../prepare-robolectric.gradle'
 
 android {
     compileSdkVersion 23
-    buildToolsVersion "23.0.1"
+    buildToolsVersion "25"
 
     defaultConfig {
         minSdkVersion 16