moment().add(period, number) is deprecated from moment 2.8.x.

since moment().add(period, number) is deprecated from moment 2.8.x. 

update related code with moment().add(number, period)  to avoid warning message.

reference: <https://github.com/moment/moment/blob/c4c47a7793dfc116acd1356f668eb1a182e29d68/min/moment-with-locales.js#L541>