Beds: Replace hardcoded values of day interval with constants

* backported https://github.com/minetest/minetest_game/pull/2990
* backported commit 2e8ac46120

mods/beds/functions.lua

@@ -258,7 +258,7 @@ function beds.on_rightclick(pos, player)
 	local ppos = player:get_pos()
 	local tod = minetest.get_timeofday()
 
-	if tod > 0.2 and tod < 0.805 then
+	if tod > beds.day_interval.start and tod < beds.day_interval.finish then
 
 		if beds.player[name] then
 			lay_down(player, nil, nil, false)

mods/beds/init.lua

@@ -43,6 +43,11 @@ beds.is_50 = is_50
 beds.is_53 = is_53
 beds.is_54 = is_54
 
+beds.day_interval = {
+	start = 0.2,
+	finish = 0.805,
+}
+
 local modpath = minetest.get_modpath("beds")
 
 -- check for minetest 5.x/0.4 compatibility