Incorrect value when adding week to date and crossing PST daylight savings

[fpintos]

Moment-timezone version which you use:

Version: "moment-timezone": "0.5.39" and "0.5.21"

Issue description:

Hello,

I want to confirm if I'm using something incorrectly or if there is an issue:

Adding a week to 2018-03-04T02:00:00-08:00 in PST gives me different results in moment, browser's Date and dotnet.

For example, with 5.39:

var moment = require("moment-timezone");
console.log(
  moment.utc("2018-03-04T02:00:00-08:00").tz("America/Los_Angeles").add(1, "weeks").toISOString(true)
);

OUTPUTS "2018-03-11T02:00:00.000-07:00"  <- Notice the "2AM" and "-7:00".

With 5.21:

OUTPUTS: "2018-03-11T01:00:00.000-08:00"  <- Notice the "1AM" and "-8:00".

However, browsers in a machine running PST, give a different date if we add 7-days' worth of milliseconds:

new Date(new Date("2018-03-04T02:00:00-08:00").getTime() + 604800000)
OUTPUTS: "Sun Mar 11 2018 03:00:00 GMT-0700 (Pacific Daylight Time)"  <- Notice the "3AM" and "-7:00"

dotnet seems to agree with the 3AM value (in a machine running PST):

TimeZoneInfo.ConvertTime(DateTimeOffset.Parse("2018-03-04T02:00:00-08:00").AddDays(7), TimeZoneInfo.Local).ToString("o")
OUTPUTS: "2018-03-11T03:00:00.0000000-07:00"  <- Notice the "3AM" and "-7:00"

Two questions:

• why values returned by moment changed between 5.21 and 5.39? change in timezone data?
• why values returned by moment do not match what browsers and dotnet return?

Thanks