Add date convert

[yacthMon]

I just add date convert, So lua script can update or insert date via os.time()
with format "day(" .. os.time() .. ")".

Example

exports.mongodb:updateOne({
   collection="users",
   query = { _id = result[1]._id },
   update = { ["$set"] = {  last_login = "day(" .. os.time() .. ")" } } 
})

This will convert last_login from "day(1554755493)" to ISODate('2019-04-08T20:31:33.000Z').

Hope this will improve this resource.

PS. I apologize if there are any errors.