Remove randomized fails in specs cause some miss configuration.

Depending on the order of the specs the notifier was configured or not. I've tried with seeds: 51050 and 19971. Seems to be solved in local.

I've moved configuration methods to a shared_context. We can reconfigure the notifier with metadata using `reconfigure_notifier: true`.
Change access_token for tests.
Change key: value syntax to hash rockets (=>).
Merge pull request #156 from rollbar/fix-random-spec-crashes

Remove randomized fails in specs cause some miss configuration.