text: Title: packaging is a required dependency
  Body: ```
  2020-02-07 04:15:34,466 [INFO ] W-9000-model-stdout com.amazonaws.ml.mms.wlm.WorkerLifeCycle -     import gluonnlp as nlp
  2020-02-07 04:15:34,466 [INFO ] W-9000-model-stdout com.amazonaws.ml.mms.wlm.WorkerLifeCycle -   File "/usr/local/lib/python3.6/site-packages/gluonnlp/__init__.py", line 49, in <module>
  2020-02-07 04:15:34,466 [INFO ] W-9000-model-stdout com.amazonaws.ml.mms.wlm.WorkerLifeCycle -     utils.version.check_version('1.6.0', warning_only=True, library=mxnet)
  2020-02-07 04:15:34,466 [INFO ] W-9000-model-stdout com.amazonaws.ml.mms.wlm.WorkerLifeCycle -   File "/usr/local/lib/python3.6/site-packages/gluonnlp/utils/version.py", line 43, in check_version
  2020-02-07 04:15:34,466 [INFO ] W-9000-model-stdout com.amazonaws.ml.mms.wlm.WorkerLifeCycle -     from packaging.version import parse
  2020-02-07 04:15:34,467 [INFO ] W-9000-model-stdout com.amazonaws.ml.mms.wlm.WorkerLifeCycle - ModuleNotFoundError: No module named 'packaging'
  ```
  
  CC @eric-haibin-lin 