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.
style: declare var at top
Merge pull request #1708 from ptbrowne/perf-makeDateFromInput

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