Fix test failure of enrollment-guide API

Reviewed-on: community/device-mgt-plugins#13

components/mobile-plugins/android-plugin/org.wso2.carbon.device.mgt.mobile.android.api/src/test/java/org/wso2/carbon/mdm/services/android/mocks/DeviceManagementProviderServiceMock.java

@@ -370,6 +370,11 @@ public class DeviceManagementProviderServiceMock implements DeviceManagementProv
 
     }
 
+    @Override
+    public void sendEnrolmentGuide(String enrolmentGuide) throws DeviceManagementException {
+
+    }
+
     @Override
     public void sendRegistrationEmail(EmailMetaInfo emailMetaInfo)
             throws DeviceManagementException, ConfigurationManagementException {