docs: API: update Mastodon API link

docs/API/differences_in_mastoapi_responses.md

@@ -46,7 +46,7 @@ The `id` parameter can also be the `nickname` of the user. This only works in th
 Has these additional fields under the `pleroma` object:
 
 - `tags`: Lists an array of tags for the user
-- `relationship{}`: Includes fields as documented for Mastodon API https://docs.joinmastodon.org/api/entities/#relationship
+- `relationship{}`: Includes fields as documented for Mastodon API https://docs.joinmastodon.org/entities/relationship/
 - `is_moderator`: boolean, nullable,  true if user is a moderator
 - `is_admin`: boolean, nullable, true if user is an admin
 - `confirmation_pending`: boolean, true if a new user account is waiting on email confirmation to be activated