Rename bootstrap-typehead.css to bootstrap-typeahead.css

The renaming could be pushed further.
In the xeditable repo the bootstrap typeaheadjs input-ext files are named:

https://github.com/vitalets/x-editable/blob/master/dist/inputs-ext/typeaheadjs/lib/typeahead.js-bootstrap.css
https://github.com/vitalets/x-editable/blob/master/dist/inputs-ext/typeaheadjs/typeaheadjs.js

This is confusing if you read the official documentation.