drop python3.6 support

python 3.6 reached end of life on 2021-12-23

Committed via https://github.com/asottile/all-repos

tests/requirements_txt_fixer_test.py

diff --git a/tests/requirements_txt_fixer_test.py b/tests/requirements_txt_fixer_test.py
index e3c6ed5..b725afa 100644
--- a/tests/requirements_txt_fixer_test.py
+++ b/tests/requirements_txt_fixer_test.py
@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 import pytest
 
 from pre_commit_hooks.requirements_txt_fixer import FAIL