The typeof x === "number" guard has stopped working

[d180cf]

After upgrading from 1.8.10 to 2.0.0 got this error:

        add(layer: matrix | number, rand = () => Math.random()) {
            const v = this.outputs[this.outputs.length - 1];

            if (typeof layer === 'number') {
                this.add(matrix.make(layer, v.length, () => rand() / layer * 2));
            } else {
                this.weights.push(layer);
                this.outputs.push(vector.zero(layer.length));
            }
        }

In the rand() / layer * 2 expression layer has type matrix | number and thus tsc complains about the arithmetic operation. The <any> type cast works around the problem.

[mhegazy]

Duplicate of #7662