remove unneccessary offensive language :hug: (#910)

Author: gr2m

source/includes/_errors.md

@@ -9,7 +9,7 @@ The Kittn API uses the following error codes:
 
 Error Code | Meaning
 ---------- | -------
-400 | Bad Request -- Your request sucks.
+400 | Bad Request -- Your request is invalid.
 401 | Unauthorized -- Your API key is wrong.
 403 | Forbidden -- The kitten requested is hidden for administrators only.
 404 | Not Found -- The specified kitten could not be found.