Update Q.d.ts with optional onRejected parameter

Spread method does not require onRejected param.
From Q documentation:
function eventualAdd(a, b) {
    return Q.spread([a, b], function (a, b) {
        return a + b;
    })
}
Merge pull request #3090 from sebastien-de-saint-florent/patch-1

Update Q.d.ts with optional onRejected parameter