Bug 915144 - [marionette-js-client] Publish the document on the Web

Doing 'doc-publish' command might have issue with .gitignore file in
https://github.com/mozilla-b2g/marionette-js-client/blob/master/.gitignore#L4.

For now, after we do 'doc-publish', it will show 'no files added'.

Force adding the api-docs folder in the commit for fixing the issue.

http://bugzil.la/915144