Fix jsdocs for multi-line ES6-style methods

Summary:
The function definition and body can be in different places for multi-line declarations, so the docblock might not get pulled in. None of the existing docs seem to be affected, but putting up the fix for posterity.

Test Plan:
I modified `AlertIOS.alert` (in Libraries/Utilties/AlertIOS.js) to actually have a docblock, and ran `website/publish.sh` (with the push bit commented out). The added doc doesn't get picked up with the current code, but it does with the fix.