Changed distance query to take double instead of int

Needed a fix for my project to allow floating point values for distance (which is supported by SOLR). Not sure if there was a valid reason to have it as an int, but I went ahead and changed it to double. All tests pass. I suppose this could potentially break users' unit tests if they are mocking and have expectations/setups that explicitly reference "int" as the type of this param, but I think that's not likely, and an easy fix anyway.