GLTFExporter Doc: Add forceIndices option

docs/examples/exporters/GLTFExporter.html

@@ -81,6 +81,7 @@ exporter.parse( [ scene1, object1, object2, scene2 ], ...)
 			<li>binary - bool. Export in binary (.glb) format, returning an ArrayBuffer. Default is false.</li>
 			<li>embedImages - bool. Export with images embedded into the glTF asset. Default is true.</li>
 			<li>animations - Array<[page:AnimationClip AnimationClip]>. List of animations to be included in the export.
+			<li>forceIndices - bool. Generate indices for non-index geometry and export with it. Default is false.</li>
 		</ul>
 		</div>
 		<div>