Added GridHelper to docs/list.js. Fixes #3868.

docs/list.js

@@ -177,6 +177,7 @@ var list = {
 			[ "AxisHelper", "api/extras/helpers/AxisHelper" ],
 			[ "CameraHelper", "api/extras/helpers/CameraHelper" ],
 			[ "DirectionalLightHelper", "api/extras/helpers/DirectionalLightHelper" ],
+			[ "GridHelper", "api/extras/helpers/GridHelper" ],
 			[ "HemisphereLightHelper", "api/extras/helpers/HemisphereLightHelper" ],
 			[ "PointLightHelper", "api/extras/helpers/PointLightHelper" ],
 			[ "SpotLightHelper", "api/extras/helpers/SpotLightHelper" ]