Upgrade to latest Android gradle plugin

// FREEBIE
Closes #1660

build.gradle

@@ -3,7 +3,7 @@ buildscript {
         mavenCentral()
     }
     dependencies {
-        classpath 'com.android.tools.build:gradle:0.11.+'
+        classpath 'com.android.tools.build:gradle:0.12.+'
         classpath files('libs/gradle-witness.jar')
     }
 }

library/build.gradle

@@ -4,7 +4,7 @@ buildscript {
     }
 
     dependencies {
-        classpath 'com.android.tools.build:gradle:0.11.+'
+        classpath 'com.android.tools.build:gradle:0.12.+'
     }
 }