new "Flow" URL (#838)

content/docs/typechecking-with-proptypes.md

@@ -12,7 +12,7 @@ redirect_from:
 >
 >We provide [a codemod script](/blog/2017/04/07/react-v15.5.0.html#migrating-from-reactproptypes) to automate the conversion.
 
-As your app grows, you can catch a lot of bugs with typechecking. For some applications, you can use JavaScript extensions like [Flow](https://flowtype.org/) or [TypeScript](https://www.typescriptlang.org/) to typecheck your whole application. But even if you don't use those, React has some built-in typechecking abilities. To run typechecking on the props for a component, you can assign the special `propTypes` property:
+As your app grows, you can catch a lot of bugs with typechecking. For some applications, you can use JavaScript extensions like [Flow](https://flow.org/) or [TypeScript](https://www.typescriptlang.org/) to typecheck your whole application. But even if you don't use those, React has some built-in typechecking abilities. To run typechecking on the props for a component, you can assign the special `propTypes` property:
 
 ```javascript
 import PropTypes from 'prop-types';