Fix test failure after 8pm

[werebus]

My browser is in the EDT time zone. But in UTC it's already tomorrow. So Time.zone.today.day returns a different number than the calendar on the site.

Failing test locally:

screaming-dinosaur/spec/system/assignment/index_spec.rb

Lines 39 to 43 in 1ba508a

	it 'highlights today' do
	visit roster_assignments_path(roster)
	today = Time.zone.today.day
	expect(page).to have_selector('td.fc-day-today', text: today)
	end

[werebus]

Won't be able to see if this works until #288 is fixed.