Bump moment from 2.17.1 to 2.21.0

[dependabot-preview]

Bumps moment from 2.17.1 to 2.21.0.

Changelog

Sourced from moment's changelog.

2.21.0 See full changelog

• Release Mar 2, 2018

• #4391 [bugfix] Fix #4390: use offset properly in toISOString

• #4310 [bugfix] Fix #3883 lazy load parentLocale in defineLocale, fallback to global if missing

• #4085 [misc] Print console warning when setting non-existent locales

• #4371 [misc] fix deprecated rollup options

• New locales: ug-cn, en-il, tg

• Various locale improvements

2.20.1 See changelog

• Release Dec 18, 2017

• #4359 [locale] Fix Arabic locale for months (again)

• #4357 [misc] Add optional parameter keepOffset to toISOString

2.20.0 See full changelog

• Release Dec 16, 2017

• #4312 [bugfix] Fix #4251: Avoid RFC2822 in utc() test

• #4240 [bugfix] Fix incorrect strict parsing with full-width parentheses

• #4341 [feature] Prevent toISOString converting to UTC (issue #1751)

• #4154 [feature] add format constants to support output to HTML5 input type formats (see #3928)

• #4143 [new locale] mt: Maltese language

• #4183 [locale] Relative seconds i18n

• Various other locale improvements

2.19.4 See changelog

• Release Dec 10, 2017

• #4332 [bugfix] Fix weekday verification for UTC and offset days (fixes #4227)

• #4336 [bugfix] Fix #4334: Remove unused function call argument

• #4246 [misc] Add 'ss' relative time key to typescript definition

2.19.3 See changelog

• Release Nov 29, 2017

• #4326 [bugfix] Fix for ReDOS vulnerability (see #4163)

• #4289 [misc] Fix spelling and formatting for U.S. for es-us

2.19.2 See changelog (it's the same >:D)

• Release Nov 11, 2017

• #4255 [bugfix] Fix year setter for random days in a leap year, fixes #4238
  ... (truncated)

Commits

• ca4ff20 Further style correction.
• 739ba8a Revert "Further style correction."
• 3a9451c Update relative_time.js
• 85e9b63 Update parsing-flags.js
• 338ebee Update from-string.js
• 332db3b Update from-string.js
• d07c05d Update from-string.js
• 108d006 Update from-string.js
• 55583a7 rfc2822 ParsingFlags moved to the bottom of the parsing code.
• e58c42b Positive and Negative RFC2822 testCases streamlined.
• Additional commits viewable in compare view

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[coveralls]

Coverage remained the same at 96.203% when pulling cd9cf04 on dependabot/npm_and_yarn/moment-2.21.0 into 6ea29b1 on master.