Improved consistancy

Lol not really i changed one line, that was distracting :)
Fixes #543: Import of wtforms _unset_value needs to change to unset_value
Force wtforms dependency version
Merge pull request #540 from psykzz/patch-1

Improved consistancy
Merge pull request #544 from Jaza/master

Fixes #543: Import of wtforms _unset_value needs to change to unset_value
Update travis.txt