Some return types don't include null

[Stuk]

The return type for some functions does not include null:

gl-matrix/src/mat4.js

Lines 286 to 293 in 4480752

	/**
	* Inverts a mat4
	*
	* @param {mat4} out the receiving matrix
	* @param {ReadonlyMat4} a the source matrix
	* @returns {mat4} out
	*/
	export function invert(out, a) {

when in actuality they can return null:

gl-matrix/src/mat4.js

Lines 328 to 330 in 4480752

	if (!det) {
	return null;
	}

This can lead to unexpected runtime errors.

[factscub]

i would like to work on this issue. please assign me.