Enable redis-cli access to RedisToGo

Accomplish the functionality described in
https://github.com/croaky/parity/issues/8. Using `Open3` from the standard
library to capture the output of the request to Heroku for the URL, which is
then memoized and parsed with regex to get the host, post, and password.

User can then access their RedisToGo with `production redis-cli`.