No hot reloading when port occupied

[croissong]

Hot reloading does not work when choosing yes for

Would you like to run the app at another port instead?

[KyleAMathews]

I noticed that the other day... would be an easy PR if you want to take it on! It looks the new port just needs set on program as well here

gatsby/lib/utils/develop.js

Line 205 in 9749910

launchPort = _port

[KyleAMathews]

Or actually... I need to make a quick release this morning anyways so I'll make the fix.