timers: fix issue #8065.

When backporting f8193ab into v0.10, a regression was introduced. Timers
with non-integer timeout could trigger a infinite recursion with 100%
cpu usage. This commit backports 93b0624 which fixes the regression.

After backporting f8193ab, instead of using Date.now(), timers would use
Timer.now() to determine if they had expired. However, Timer.now() is
based on loop->time, which is not updated when a timer's remaining time
is > 0 and < 1. With this commit, Timer.now() updates loop->time itself.