Add request specs for short URL redirects
Add request specs for short URL redirects

- For a valid short URL, ensure that we respond with a 302 redirect
- For an invalid short URL, ensure that we respond with a 404

codeunion/url-shortener,codeunion/url-shortener,jfarmer/url-shortener,jfarmer/url-shortener,jfarmer/url-shortener,chrisswk/url-shortener,chrisswk/url-shortener,codeunion/url-shortener,chrisswk/url-shortener