fix for auto-generated casette name when "it" block in rspec has no description

```ruby
decribe A do
  descirbe 'test', vcr: true do
    before { do_some_http_request }
    subject { true }
    it { should be_true }
  end
end
```

This example generates file with name `spec/vcr_cassettes/A/test/.yml` but should generate `spec/vcr_cassettes/A/test.yml`