UniformUtils: Also clone Matrix3. See #6309.

src/renderers/shaders/UniformsUtils.js

@@ -40,6 +40,7 @@ THREE.UniformsUtils = {
 					 parameter_src instanceof THREE.Vector2 ||
 					 parameter_src instanceof THREE.Vector3 ||
 					 parameter_src instanceof THREE.Vector4 ||
+					 parameter_src instanceof THREE.Matrix3 ||
 					 parameter_src instanceof THREE.Matrix4 ||
 					 parameter_src instanceof THREE.Texture ) {