Update relax.php to fix submission of an array of keys 

The build_url function had two issues:
- when calling a view with multiple keys, it would fall to the "else" branch which is undesirable.
- when submitting an array, it didn't add an ampersand after the array, which would provide couch an improper get request (e.g. &keys=[1,2,3]include_docs='true')