Adds failing case for failing dd/m/yyyy.

Hi, I've began working on a [haskell library](https://github.com/mavenraven/chronic-haskell) that provides similar functionality as Chronic. I've been going through and porting the test cases, and I noticed that

    "30/2/2000"

is not supposed to parse, but

    "27/5/1979"

is. I plan on supporting both cases, and it seems like it's a bug for the first case not to work.