Update specs to work with rspec 3.0.x syntax

Ran the specs and saw some deprecation warnings with rspec 3.0.0

```
Using `should` from rspec-expectations' old `:should` syntax without explicitly enabling the syntax is deprecated. Use the new `:expect` syntax or explicitly enable `:should` instead.
```

So updated the spec syntax to work with rspec 3, thanks for the helpful gem, hope this helps!