Bug in endOf in any months with 31 days

[etruta]

Detailed Description

When I use the moment().endOf("M") in many 31 days months, as December, the return is the day 30th.

moment().endOf("M").format("dd/MM/YYYY") return 30/12/2017

Context

I use this to show the start and end of a month report

Environment

• Version used: 0.7

[etruta]

Add a month in months with 31 days too have problem when use the moment().startOf("M").

(moment().startOf("M") + 1.months).format("dd/MM/YYYY") return 31/12/2017 when the correct is 01/01/2018.

Maybe, this problem cause de endOf problem.