Change name in bower.json from "pjax" to "jquery-pjax"

The name of the package should match the name it is registered as in
Bower. Since this package is registered as "jquery-pjax", the name
should be that. This is also consistent with the name of the repo.
Merge pull request #385 from causes/bower-name

Change name in bower.json from "pjax" to "jquery-pjax"