Merge pull request #16591 from aardgoose/docs

document capabilities.isWebGL2

docs/api/en/renderers/WebGLRenderer.html

@@ -113,6 +113,7 @@
 		- [page:Boolean floatVertexTextures]: *true* if [page:Boolean floatFragmentTextures] and [page:Boolean vertexTextures] are both true.<br />
 		- [page:Method getMaxAnisotropy](): Returns the maximum available anisotropy.<br />
 		- [page:Method getMaxPrecision](): Returns the maximum available precision for vertex and fragment shaders. <br />
+		- [page:Boolean isWebGL2: *true* if the context in use is a WebGL2RenderingContext object.<br />
 		- [page:Boolean logarithmicDepthBuffer]: *true* if the [page:parameter logarithmicDepthBuffer] was set to true in the constructor and
 		the context supports the [link:https://developer.mozilla.org/en-US/docs/Web/API/EXT_frag_depth EXT_frag_depth] extension.
 			According to [link:https://webglstats.com/ WebGLStats], as of February 2016 around 66% of WebGL enabled devices support this.<br />