Nlpaug

* Update MANIFECT file to include txt resource

* Add back English mispelling dictionary

* Fix PPDB model misloaded nltk module[144](https://github.com/makcedward/nlpaug/issues/144)

* Enhance default tokenizer and reverse tokenizer[143](https://github.com/makcedward/nlpaug/issues/143)
* Introduce Abstractive Summarization in sentence ausgmenter (Check out example from [here](https://github.com/makcedward/nlpaug/blob/master/example/textual_augmenter.ipynb))

Fix [142](https://github.com/makcedward/nlpaug/issues/142)

Support crop action in RandomWordAug [126](https://github.com/makcedward/nlpaug/issues/126)
Fix [130](https://github.com/makcedward/nlpaug/issues/130)
Fix [132](https://github.com/makcedward/nlpaug/issues/132)
Fix [134](https://github.com/makcedward/nlpaug/issues/134)
Upgraded and verified torch (1.6.0) and transformers (3.0.2) libraies
Add new Back Translation Augmenter [75](https://github.com/makcedward/nlpaug/issues/75) [#102](https://github.com/makcedward/nlpaug/issues/102) [#131](https://github.com/makcedward/nlpaug/issues/131)