Auto update http://haskell.github.io/haskell-mode/manual/latest/ from TravisCI build

[gracjan]

Auto update http://haskell.github.io/haskell-mode/manual/latest/ from TravisCI build. Example how this can be done is here:

https://github.com/flycheck/flycheck/blob/master/doc/deploy-travis.bash

[gracjan]

That was done in #664.