avoid double encoding

we don't want to use toPathValue on query params because they will be encoded
anyway during callAPI and this could lead to double encoding.
Instead, just transform them into strings.

Example of current bug:
   {'foo': 'bar:baz'}
   # after urllib.quote (in toPathValue)
   {'foo': 'bar%3Abaz'}
   # after urllib.urlencode (in callAPI)
   'foo=bar%253Abaz'

   # instead it should have been:
   'foo=bar%3Abaz'
Merge branch 'master' of https://github.com/wordnik/swagger-codegen