On 1.8.7, `Kernel#Array` has a gotcha

``` irb
➜  rspec-dev git:(master) irb
irb(main):001:0> Array("foo\nbar")
=> ["foo\n", "bar"]
```

Multiline strings get split.

I don't think this is what we want -- if a single multiline string is provided, this should return an array of a single string (the entire provided string).

As an alternate implementation suggestion, consider making this an `attr_reader` and assigning `@expected_as_array` in `initialize` to the original provided `expected` array.  Then you could define an `expected` method that does the reduction to a single value if it's an array of one value, which would simplify `initialize` a bit.

Regardless, given this gotcha, it would be good to add a spec for the case of a single multiline string to guard against future regressions.