add support for RSpec 3.0.0beta2 (RSpec 2 compat)

started with 3.0.0beta2 it starts complaining with
```
Deprecation Warnings:

The Fuubar formatter uses the deprecated formatter interface.
 Formatter added at: /Users/razum2um/.rvm/gems/ruby-2.1.0/gems/rspec-core-3.0.0.beta2/exe/rspec:4:in `<top (required)>'
```
this updates lib with up-to-date upstream
tested itself on RSpec2.14 & Rspec3.0.0beta2
the gem can be still used with any rspec version (2 & 3) - no need to bump upper version