Previously calls to `in` were being sent to the non-DST aware
method `Time#since` via `method_missing`. It is now aliased to
the DST aware `ActiveSupport::TimeWithZone#+` which handles
transitions across DST boundaries, e.g:

    Time.zone = "US/Eastern"

    t = Time.zone.local(2016,11,6,1)
    # => Sun, 06 Nov 2016 01:00:00 EDT -05:00

    t.in(1.hour)
    # => Sun, 06 Nov 2016 01:00:00 EST -05:00