Update bin/dev to set port

Author: lcreid

demo/Procfile.dev

@@ -1,3 +1,3 @@
-web: bundle exec bin/rails server -p ${TEST_APP_PORT:-3000} -b 0.0.0.0
+web: bundle exec bin/rails server -b 0.0.0.0
 js: yarn build --watch
 css: yarn build:css --watch

demo/bin/dev

@@ -5,4 +5,7 @@ if ! gem list foreman -i --silent; then
   gem install foreman
 fi
 
+# Default to port 3000 if not specified
+export PORT="${PORT:-3000}"
+
 exec foreman start -f Procfile.dev "$@"