Added compatibility with Brunch's command-line tests.

[rtfeldman]

Although the nodejs branch provides standalone NodeJS test functionality, evidently all that's needed to get them working with Brunch (http://brunch.io) tests is to give canvasses a default style object. (And having jsdom and canvas installed, of course.)

Without this, trying to run Brunch tests involving Kinetic fail because Layer tries to set this.canvas.getElement().style.position = 'absolute' and evidently jsdom's implementation of canvas does not give it a default style object.

With this change, the style object is guaranteed to exist, and Brunch tests work.

[ericdrowell]

Haven't forgotten about this - will add it in as soon as I get the chance (been pretty swamped lately)

[lavrton]

I added this with nodejs support commit.