Update docs - add keyBindingFn prop to list of editor props
Update docs - add keyBindingFn prop to list of editor props

Summary:
the `keyBindingFn` prop is missing from the list of Editor Props in the docs, here it is
Closes https://github.com/facebook/draft-js/pull/1249

Differential Revision: D6111817

fbshipit-source-id: f9c059688951a9bbfc3a0d5519a228f197898524

facebook/draft-js