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).
You can check out the color implementation: https://github.com/shoes/shoes4/blob/master/lib/shoes/color.rb#L62-L69

Using `inspect` is a clever trick but it's not what it is supposed to do. Compare the real values that make up an object, I don't know those values for gradient right now but for color for instance one compares if the red, green, blue values are the same etc.