fix PixelPerfectScaleMode on html5

[Geokureli]

From Travis on Discord:

Q: does PixelPerfectScaleMode work on an html build?
I set it just like a do for a Windows build, which scales correctly when I resize that window.
But for the HTML build, when I resize the browser window, it scales continuously (not jumping between the pixel perfect resolutions)

[travisbattles]

Here's what I do for the HTML and Windows builds in the project.xml:

<!--HTML5-specific-->
<window if="html5" fullscreen="false" resizable="true" width="320" height="180" />

<!--Desktop-specific-->
<window if="desktop" orientation="landscape" fullscreen="false" resizable="true" width="320" height="180"/>

Here's Main.hx where I set the scaleMode:

class Main extends Sprite
{
	public function new()
	{
		super();
		addChild(new FlxGame(0, 0, MenuState));
		FlxG.scaleMode = new PixelPerfectScaleMode();
	}
}