Bump dependencies (#195)

* Bump TF to 1.15.2

* Bump Gensim to 3.8.1

* Remove scipy from dependency list

* Bump numpy to 1.18.2

* Bump NLTK to 3.4.5

Merge pull request #191 from inspirehep/bump-deps

Bump deps

Merge pull request #117 from inspirehep/keras-2-compatibility

Release Magpie 2.0

Merge pull request #97 from inspirehep/bump-version

Creating version 1.0