docs: fix typo in CONTRIBUTING.md (#233)

Author: nakatani-yo

CONTRIBUTING.md

@@ -12,4 +12,4 @@ Run tests locally
 npm test
 ```
 
-Learn more about how the tests work in [test/README.md](test/README.md).
+Learn more about how the tests work in [tests/README.md](tests/README.md).