feat(upgrade): Upgraded to support date-fns v2

[joanllenas]

New pipes:

• dfnsAddBusinessDays
• dfnsDifferenceInBusinessDays
• dfnsGetUnixTime
• dfnsGetWeek
• dfnsGetWeekOfMonth
• dfnsGetWeeksInMonth
• dfnsGetDecade
• dfnsGetWeekYear
• dfnsLastDayOfDecade
• dfnsStartOfDecade
• dfnsStartOfWeekYear

BREAKING CHANGE:

• Library is now Angular >= v8 only.
• Pipe argument validations are now done by date-fns.
• Renamed dfnsAddISOYears to dfnsAddISOWeekYears.
• Renamed dfnsDifferenceInCalendarISOYears to dfnsDifferenceInCalendarISOWeekYears.
• Renamed dfnsDifferenceInISOYears to dfnsDifferenceInISOWeekYears.
• Renamed dfnsDistanceInWords to dfnsFormatDistance. Also, notice that date arguments have been swapped to be consistent with date-fns.
• Renamed dfnsDistanceInWordsStrict to dfnsFormatDistanceStrict. Also, notice that date arguments have been swapped to be consistent with date-fns. See https://date-fns.org/v2.0.1/docs/formatDistanceStrict#v2.0.0-breaking-changes for more breaking changes related to the options param.
• Renamed dfnsDistanceInWordsToNow to dfnsFormatDistanceToNow.
• Renamed dfnsEndOfISOYear to dfnsEndOfISOWeekYear.
• Renamed dfnsGetISOYear to dfnsGetISOWeekYear
• Renamed dfnsGetOverlappingDaysInRanges to dfnsGetOverlappingDaysInIntervals. Also, time interval arguments are passed differently: See https://date-fns.org/v2.0.1/docs/getOverlappingDaysInIntervals#v2.0.0-breaking-changes for more info.
• Renamed dfnsLastDayOfISOYear to dfnsLastDayOfISOWeekYear.
• Renamed dfnsStartOfISOYear to dfnsStartOfISOWeekYear
• Renamed dfnsSubISOYears to dfnsSubISOWeekYears
• In general, all date-fns changes (lots of changes) also apply to this library. See https://github.com/date-fns/date-fns/blob/master/docs/upgradeGuide.md and https://github.com/date-fns/date-fns/blob/master/CHANGELOG.md#200---2019-08-20 for the whole upgrade guide.