[MobileClient] Add android support annotations dependency

Author: minbi

aws-android-sdk-mobile-client/pom.xml

@@ -38,6 +38,12 @@
       <type>aar</type>
     </dependency>
 
+    <dependency>
+      <groupId>com.android.support</groupId>
+      <artifactId>support-annotations</artifactId>
+      <version>27.1.1</version>
+    </dependency>
+
     <dependency>
       <groupId>com.amazonaws</groupId>
       <artifactId>aws-android-sdk-cognitoidentityprovider</artifactId>