fix: Don't use negative integers to slice

Author: FloatingGhost

graphene_mongo/fields.py

@@ -142,7 +142,7 @@ def get_query(cls, model, info, **args):
                 objs = objs[:first]
             if last is not None:
                 # https://github.com/graphql-python/graphene-mongo/issues/20
-                objs = objs[-(last+1):]
+                objs = objs[list_length - last:]
         else:
             list_length = objs.count()