fix(testing): create_environ does not decode the path

WSGI servers decode the path submitted in the request before passing it
to the app via the PATH_INFO environ field (wsgiref, uWSGI, and gunicorn
were tested to verify this behavior). This patch updates create_environ
to behave similarly.
Merge pull request #341 from kgriffs/environ

fix(testing): create_environ does not decode the path