Use ruamel.yaml for readme_test

tests/readme_test.py

diff --git a/tests/readme_test.py b/tests/readme_test.py
index b2d03b3..fd6d265 100644
--- a/tests/readme_test.py
+++ b/tests/readme_test.py
@@ -3,7 +3,7 @@
 
 import io
 
-import yaml
+from pre_commit_hooks.check_yaml import yaml
 
 
 def test_readme_contains_all_hooks():