Update MapQuest spec to use `subject` and `it`

For brevity and ease of reading I've updated MapQuest spec to lean less on `let` and more on explicit `subject`s and implicit `it` expectations. I've also removed some unnecessary argument-related tests as they were just testing ruby's default parameter handling behaviour.
Merge pull request #2 from liveline/spec_tidy

Update MapQuest spec to use `subject` and `it`