Docs: update link in pagination.py (#5321)

The blog post referenced in the documentation has been since moved to a new location.

rest_framework/pagination.py

@@ -473,7 +473,7 @@ class CursorPagination(BasePagination):
     """
     The cursor pagination implementation is necessarily complex.
     For an overview of the position/offset style we use, see this post:
-    http://cramer.io/2011/03/08/building-cursors-for-the-disqus-api
+    http://cra.mr/2011/03/08/building-cursors-for-the-disqus-api
     """
     cursor_query_param = 'cursor'
     cursor_query_description = _('The pagination cursor value.')