Bumping to version 2.1.7.

Closes kylebgorman#86.

Merge pull request kylebgorman#81 from kylebgorman/v2.1.6.post1

v2.1.6.post1

Merge pull request kylebgorman#74 from kylebgorman/v2.1.6

Pynini release v2.1.6

Merge pull request kylebgorman#73 from kylebgorman/v2.1.5.post2

v2.1.5.post2

fix requirements.txt

update dockerfile to 2.1.5.post1