Update docs to reflect change to default setting of 'alpha' from true to false...

Update docs to reflect change to default setting of 'alpha' from true to false made in 0ade4a1d.

docs/api/renderers/WebGLRenderer.html

@@ -23,7 +23,7 @@
 		<div>
 		canvas — A [page:Canvas] where the renderer draws its output.<br />
 		precision — shader precision. Can be *"highp"*, *"mediump"* or *"lowp"*.<br />
-		alpha — [page:Boolean], default is *true*.<br />
+		alpha — [page:Boolean], default is *false*.<br />
 		premultipliedAlpha — [page:Boolean], default is *true*.<br />
 		antialias — [page:Boolean], default is *false*.<br />
 		stencil — [page:Boolean], default is *true*.<br />