perf(makeDateFromInput): no need to match regex if input is a Date

The moment constructor when passed a Date should be the fastest. There is
no need to match the aspNetJsonRegex before testing if the `input` is a
Date.
I don't know why jshint doesn't scream about that, but each function should have only one var at the top. Just declare it at the top and define it here. `matched` can also be set inside the if statement (its only used inside).