Bump gradle version to appease Android Studio.

I see a "we recommend you upgrade" message on every gradle file sync.
This gets rid of the nagging.

BUG=620034

Review-Url: https://codereview.chromium.org/2577493003
Cr-Original-Commit-Position: refs/heads/master@{#438291}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 6248702a749585cf219e929e29f26efc207fc233

android/gradle/build.gradle.jinja

@@ -9,7 +9,7 @@ buildscript {
         jcenter()
     }
     dependencies {
-        classpath "com.android.tools.build:gradle:2.2.0"
+        classpath "com.android.tools.build:gradle:2.2.1"
     }
 }