Don't coerce PORT into an integer unless you need to

With Foreman 0.63, the PORT env var that it creates would cause Clojure to melt down when calling `(Integer/parseInt env-var)`.

Calling Integer/parseInt on an integer throws this exception:

```clojure
(Integer/parseInt 5000)
;; java.lang.ClassCastException: java.lang.Long cannot be cast to java.lang.String
```

This just checks for an int before calling that. Foreman starts the web server correctly now. Thanks!