Set 'rake install' as the default task

Seemed like a reasonable thing since every time I clone CedarShortcuts I just want to install, and I forget that there isn't a default rake task, but feel free to ignore / close if you disagree.

While I'm typing these words, I just wanted to say that this project is awesome. Saves a ton of time when I'm looking at cedar test failures. Thank you so much for open sourcing this!