Function covid19db::dateutil::ymd_to_nd

pub fn ymd_to_nd(year: i32, month: u32, day: u32) -> NaiveDate

Convert a year, month, day to a NaiveDate

use covid19db::dateutil::*;
use chrono::prelude::*;

assert_eq!(ymd_to_nd(2015, 3, 14), NaiveDate::from_ymd(2015, 3, 14));