Bumping to version 2.1.7. Closes #86.
Merge pull request #81 from kylebgorman/v2.1.6.post1 v2.1.6.post1
Merge pull request #74 from kylebgorman/v2.1.6 Pynini release v2.1.6
Merge pull request #73 from kylebgorman/v2.1.5.post2 v2.1.5.post2