Fix case-insensitive stop-refering

stop-referring did a find-replace based off global preference for case
sensitivity. However, clojure vars are case sensitive, so it doesn't
make sense to respect global preference. 

What was happening to me was I
had an ns with `(:require [schema.core :as schema :refer [Str]))` which
was replacing both calls like `{schema/Any Str` to `{schema/Any
schema/Str}` as well as calls like `(str 25)` to `(schema/str 25)`