add function to get day of month

[ritzjp]

trafficstars

Some time it need to have the day of month I have add this function getDayOfMonth can you add it to the project

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}