Set 3000 as the default web port

Having by default `PORT=` only assigns to that variable `0`, which is
interpreted by puma to start the web app in a random port when `bin/dev`
is called. Also `export`ing the port in this file is useless, as in the
foreman context, it's eventually overriden by the settings of your default
`.env` file that has just been copied from `.env.example`.

.env.example

@@ -1,6 +1,6 @@
 # Custom port config
 # For users who have other applications listening at 3000, this allows them to set a value puma will listen to.
-PORT=
+PORT=3000
 
 # Exchange Rate API
 # This is used to convert between different currencies in the app. We use Synth, which is a Maybe product. You can sign up for a free account at synthfinance.com.

bin/dev

@@ -5,9 +5,6 @@ if ! gem list foreman -i --silent; then
   gem install foreman
 fi
 
-# Default to port 3000 if not specified
-export PORT="${PORT:-3000}"
-
 # Let the debug gem allow remote connections,
 # but avoid loading until `debugger` is called
 export RUBY_DEBUG_OPEN="true"