Add some specs for the progress formatter
Fix scenario

We need to use the pretty formatter because we're now actually handling
and printing the before hook exception in the formatter, where Cucumber
1.x was just throwing the exception and stopping Cucumber in its tracks.

Progress formatter doesn't print exception messages (though perhaps it
should?) so we need to use pretty.
Big moment: First beta release of Cucumber 2.0

Thanks @tooky @brasumssen @os97673 @jimvm @tom025 and everyone else who
helped to get this release ready.