Leaderboard widget custom dates using incorrect hour/min

[nrotstan]

When using custom dates on the Leaderboard Widget (e.g. when managing a challenge), the frontend appears to be converting the current hour/minute to UTC for transmission to the server instead of converting local midnight.

For example, when at 10:22am PST I did a custom date range of March 2 - March 4, the frontend submitted to the server:

start: 2021-03-02T18:22:05.000Z
end: 2021-03-04T18:22:11.000Z