fix: typo in cleanup link (#672)

Author: cncolder

docs/react-testing-library/setup.mdx

@@ -295,7 +295,7 @@ install @babel/polyfill (if you're using babel 7) or babel-polyfill (for babel
 
 ### Skipping Auto Cleanup
 
-[`Cleanup`](./api#cleanup) is called after each test automatically by default if
+[`Cleanup`](api.mdx#cleanup) is called after each test automatically by default if
 the testing framework you're using supports the `afterEach` global (like mocha,
 Jest, and Jasmine). However, you may choose to skip the auto cleanup by setting
 the `RTL_SKIP_AUTO_CLEANUP` env variable to 'true'. You can do this with