lib/time, time/tzdata: update tz data to 2020a

Updates #22487

Change-Id: I691b4c8ced7bfb368f46ade0be46b2ab3f1820dd
Reviewed-on: https://go-review.googlesource.com/c/go/+/230360
Run-TryBot: Tobias Klauser <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>

Author: tklauser

lib/time/update.bash

@@ -8,8 +8,8 @@
 # Consult https://www.iana.org/time-zones for the latest versions.
 
 # Versions to use.
-CODE=2019c
-DATA=2019c
+CODE=2020a
+DATA=2020a
 
 set -e
 rm -rf work