android {
    compileSdkVersion 21
    buildToolsVersion "21.1.0"

    defaultConfig {
        ...
        minSdkVersion 14
        targetSdkVersion 21
        ...

        // Enabling multidex support.
        multiDexEnabled true
    }
    ...
}

dependencies {
    compile 'com.android.support:multidex:1.0.0'
}

public class GlobalApplication extends MultiDexApplication {
    @Override
    protected void attachBaseContext(Context base) {
        super.attachBaseContext(base);
        MultiDex.install(this);
    }
}