Fixed 'clear' method's description

WebGLRenderer's documentation incorrectly stated that if no parameters were passed to it, the 'clear' method will not clear any buffers. The default behaviour is in fact the opposite: if an argument is undefined, the corresponding buffer will be cleared. The document now correctly describes the default behaviour.
Source code of the method: https://github.com/mrdoob/three.js/blob/master/src/renderers/WebGLRenderer.js#L368

docs/api/renderers/WebGLRenderer.html

@@ -218,7 +218,7 @@
 
 		<h3>.clear( [page:Boolean color], [page:Boolean depth], [page:Boolean stencil] )</h3>
 		<div>Tells the renderer to clear its color, depth or stencil drawing buffer(s).</div>
-		<div>If no parameters are passed, no buffer will be cleared.</div>
+		<div>Arguments default to true.</div>
 
 		<h3>.addPostPlugin( plugin )</h3>
 		<div>Initialises the postprocessing plugin, and adds it to the renderPluginsPost array.</div>