Handle JSON decode error

flask_discord/exceptions.py

@@ -1,3 +1,6 @@
+import json
+
+
 class HttpException(Exception):
     """Base Exception class representing a HTTP exception."""
 
@@ -24,11 +27,16 @@ class RateLimited(HttpException):
 
     def __init__(self, response):
         self.response = response
+        try:
             self.json = self.response.json()
+        except json.JSONDecodeError:
+            self.json = dict()
+            self.message = self.response.text
+        else:
             self.message = self.json["message"]
             self.is_global = self.json["global"]
             self.retry_after = self.json["retry_after"]
-        super().__init__(self.json["message"])
+        super().__init__(self.message)
 
 
 class Unauthorized(HttpException):