introduce a test to show circuit breaker rate is not working.

Circuitbox rate does not work.
here the test to prove it .... :-(

running the test give the result:
```
  1) Failure:
ratio#test_0002_open the circuit even after 1 success [/Users/yarmand/Code/circuitbox/test/circuit_breaker_test.rb:58]:
the total count of failures is not 5.
Expected: 5
Actual: 0
```

WARNING: merging this pull request will break the test suite. But I think it worth it.