Updated shape to use style method

Hi again all!

This one involved a little more tweaking than the other ones. It looks like the configuration specs were using Shape (randomly?) so I had to update them to not look for a style hash since shape doesn't use it.

Tests pass and everything else was straight forward so I think this is ready to go. 

PS. I'll merge this (and others) after at least one reviewer gives me the go ahead as per (1) [here](https://github.com/shoes/shoes4/wiki/Merging-a-Pull-Request).
Minor point of style, if I'm bothering to pull out a method for this type of checking, I'd probably rename it to `check_classes` and have it do the comparison in addition to the `raise` instead of just extracting the raising. Not a big deal either way, but that would keep this method a bit tidier.