Sync zoneinfo database with tzdata2020a from ftp://ftp.iana.org/tz/releases

Sync zoneinfo database with tzdata2020a from ftp://ftp.iana.org/tz/releases

* Morocco's second spring-forward transition in 2020 will be May 31,
    not May 24 as predicted earlier.  (Thanks to Semlali Naoufal.)

* Canada's Yukon advanced to -07 year-round on 2020-03-08.

* America/Nuuk renamed from America/Godthab.

* Shanghai observed DST in 1919.  (Thanks to Phake Nick.)

* To reflect current usage in English better, America/Godthab has
    been renamed to America/Nuuk.  A backwards-compatibility link
    remains for the old name.

For a detailed list of changes, see share/zoneinfo/NEWS.