Android Studio не свива приложението ми

Опитвам се да намаля размера на моя apk (тъй като услугите на Google Play увеличиха размера на приложението ми от 65kb на 5MB), като използвам свиване, както е казано в тази мрежа: http://tools.android.com/tech-docs/new-build-system/resource-shrinking

добавих minifyEnabled true и shrinkResources true

Проблемът е, че както е казано в тази мрежа, това трябва да се показва в дневника на gradle:

:android:shrinkDebugResources
Removed unused resources: Binary resource data reduced from 2570KB to 1711KB: Removed 33%

Но нищо не се показва в дневника на gradle.... само това:

Executing tasks: [:app:assembleDebug]

Configuration on demand is an incubating feature.
:app:preBuild
:app:compileDebugNdk UP-TO-DATE
:app:preDebugBuild
:app:checkDebugManifest
:app:preReleaseBuild
:app:prepareComAndroidSupportSupportV42100Library UP-TO-DATE
:app:prepareComGoogleAndroidGmsPlayServicesAds6587Library UP-TO-DATE
:app:prepareComGoogleAndroidGmsPlayServicesBase6587Library UP-TO-DATE
:app:prepareDebugDependencies
:app:compileDebugAidl UP-TO-DATE
:app:compileDebugRenderscript UP-TO-DATE
:app:generateDebugBuildConfig UP-TO-DATE
:app:generateDebugAssets UP-TO-DATE
:app:mergeDebugAssets UP-TO-DATE
:app:generateDebugResValues UP-TO-DATE
:app:generateDebugResources UP-TO-DATE
:app:mergeDebugResources UP-TO-DATE
:app:processDebugManifest UP-TO-DATE
:app:processDebugResources UP-TO-DATE
:app:generateDebugSources UP-TO-DATE
:app:compileDebugJava UP-TO-DATE
:app:preDexDebug
:app:dexDebug
:app:processDebugJavaRes UP-TO-DATE
:app:validateDebugSigning
:app:packageDebug
:app:zipalignDebug
:app:assembleDebug

BUILD SUCCESSFUL

Total time: 37.258 sec

това е моят код:

apply plugin: 'com.android.application'

android {
    compileSdkVersion 19
    buildToolsVersion "21.1.2"

    defaultConfig {
        applicationId "com.myapp"
        minSdkVersion 14
        targetSdkVersion 19
    }

    buildTypes {
        release {
            minifyEnabled true
            shrinkResources true
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-project.txt'
        }
    }

    dependencies {
        compile 'com.google.android.gms:play-services-ads:6.5.87'
    }
}