Make Forego port match APPLICATION_HOST port
Make Forego port match APPLICATION_HOST port

Suspenders previously included a `.foreman` file which specified that
Foreman should use port 3000, and not the default of 5000 (rationale
in a42ec7e). The switch from Foreman to Forego in 6b7614a removed this
file since Forego doesn't support it, causing a reversion to port 5000
and a mismatch with the `APPLICATION_HOST` and `ASSET_HOST` variables
in the sample `.env` file.

Forego does support specifying a port via the PORT environment
variable, so this change adds that variable to the sample `.env` file.

[closes #665]
[closes #666]

Mossio/hashira-rails,lorentrogers/suspenders,toobulkeh/suspenders,kvokka/suspenders,headwayio/voyage,headwayio/voyage,headwayio/suspenders,delphaber/suspenders,brandoncordell/suspenders,kvokka/suspenders,welaika/welaika-suspenders,lorentrogers/suspenders,pacso/suspenders,Mossio/hashira-rails,headwayio/voyage,delphaber/suspenders,welaika/welaika-suspenders,pacso/suspenders,mukkoo/welaika-suspenders,mukkoo/welaika-suspenders,headwayio/suspenders,thoughtbot/suspenders,headwayio/suspenders,Mossio/hashira-rails,toobulkeh/suspenders,headwayio/suspenders,kvokka/suspenders,delphaber/suspenders,Mossio/hashira-rails,mukkoo/welaika-suspenders,thoughtbot/suspenders,toobulkeh/suspenders,zamith/suspenders,lorentrogers/suspenders,thoughtbot/suspenders,zamith/suspenders,welaika/welaika-suspenders,headwayio/voyage,pedrosmmoreira/suspenders,pedrosmmoreira/suspenders,zamith/suspenders,brandoncordell/suspenders,pacso/suspenders,pedrosmmoreira/suspenders,brandoncordell/suspenders