Fix link (#277)

Fixes the link hash

content/docs/typechecking-with-proptypes.md

@@ -10,7 +10,7 @@ redirect_from:
 >
 > `React.PropTypes` has moved into a different package since React v15.5. Please use [the `prop-types` library instead](https://www.npmjs.com/package/prop-types).
 >
->We provide [a codemod script](/blog/2017/04/07/react-v15.5.0.html#migrating-from-react.proptypes) to automate the conversion.
+>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: