* [Android] (gradle build) nullPoint fix for ndk.dir check  - issue: https://github.com/apache/incubator-weex/issues/1907
* [Android] (gradle build) nullPoint fix for ndk.dir check
 - issue: https://github.com/apache/incubator-weex/issues/1907

KalicyZhou/incubator-weex,KalicyZhou/incubator-weex,acton393/incubator-weex,acton393/incubator-weex,acton393/incubator-weex,acton393/incubator-weex,acton393/incubator-weex,acton393/incubator-weex,KalicyZhou/incubator-weex,KalicyZhou/incubator-weex,KalicyZhou/incubator-weex,alibaba/weex,alibaba/weex,alibaba/weex,alibaba/weex,alibaba/weex,acton393/incubator-weex,alibaba/weex,acton393/incubator-weex,KalicyZhou/incubator-weex,alibaba/weex