Fixes style bug in pixi renderer

This allows the default styles to be overridden in the pixi renderer:

Example:

	var renderer = Physics.renderer('pixi', {
		el: 'primitives',
		width: viewWidth,
		height: viewHeight,
		meta: true,
		styles: {			<-- This works now with this patch
			'circle' : {
				strokeStyle: '0x2d2d2dC',
				lineWidth: 3,
				fillStyle: '0xff2222',
				angleIndicator: '0xE8900C'
			}
		}
	});
	
Thanks to @aldeed for the patch!