Bug in updateLocale: resetting doesn't work

[kumarharsh]

Describe the bug
Say moment's locale is updated to have a different week.dow: moment.updateLocale(moment.locale(), { week: { dow: 4 } }). Later, if this locale is reset using moment.updateLocale(moment.locale(), null), then it's observed that the locale is not reset cleanly. I was trying to use this approach in Jest, but it's not working.

To Reproduce
Steps to reproduce the behavior:

1. Go to https://codesandbox.io/s/qqjm33km19
2. See output.

Expected behavior
The second date should have been 2018-12-30 because the default locale is 'en' and default week.dow is 0 (Sunday).

Desktop (please complete the following information):

• OS: [e.g. iOS] Windows
• Browser [e.g. chrome, safari] Chrome
• Version [e.g. 22] 71

Moment-specific environment

• The time zone setting of the machine the code is running on: en-IN
• The time and date at which the code was run: 2019-01-22 19:10
• Other libraries in use (TypeScript, Immutable.js, etc): React

Please run the following code in your environment and include the output:

console.log((new Date()).toString())
console.log((new Date()).toLocaleString())
console.log((new Date()).getTimezoneOffset())
console.log(navigator.userAgent)
console.log(moment.version)

Tue Jan 22 2019 19:09:50 GMT+0530 (India Standard Time)
1/22/2019, 7:09:50 PM
-330
Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.98 Safari/537.36
2.24.0

[ashsearle]

Yep, it's a bug.

moment's resetting the locale OK, but holding onto a global reference.

See the updated codesandbox for how to manually avoid this pending a new release with the bug fix.

[kumarharsh]

@ashsearle yeah, I accidentally observed while raising the issue that calling moment.locale('en') did in fact give me the expected result. I was just not sure if that was actually what was flushing the global reference. Thanks for the PR!