Why not just default to working? If we just throw an error here than I have to do something to get it to work. Most people aren't going to have a PORT env variable, but those that do have it for a reason. If EAK is going to use environment variables, and fail if they aren't set properly, then they should be name spaced so they avoid possible conflicts. 

It could also be argued that this doesn't belong as an ENV variable anyway and should go in the package.json since that is where other config options are like the `proxyURL`.