Fix the regexp serialization issue for scenario runner

This is simliar to Issue 119. 

Problem: If given a RegExp in toMatch and fails, {} is printed in the output. (This happens in angular-phonecat Step 03)

Fix: Use string value of the RegExp in `toJsonReplacer`.

Question: This may affect the correctness of `angular.fromJson` since `angular.fromJson(angular.toJson(/test/))` should be an `Object`. Jasmine uses their own pp method that handles RegExp in a similar way. Would it be better to fix this by introducing a simple pp method in ngScenario?

Thanks,
Gary