tools: bump gradle

Change-Id: I2ed3a5cb2cd2c500590441ba94191dbab6594c30
diff --git a/ring-android/build.gradle b/ring-android/build.gradle
index 661c833..8cb691b 100644
--- a/ring-android/build.gradle
+++ b/ring-android/build.gradle
@@ -4,7 +4,7 @@
         jcenter()
     }
     dependencies {
-        classpath 'com.android.tools.build:gradle:2.3.2'
+        classpath 'com.android.tools.build:gradle:2.3.3'
     }
 }
 allprojects {