Upgrade to tzdata2012b.

Summer time in Cuba has been delayed 3 weeks (now starts April 1 rather
than March 11). Since March 11 (the old start date, as listed in 2012a)
is just a little over a week away, this change is urgent.

Change-Id: Iadf4dc30072bdac0bcd0ad4b9e076a9ca071efbe
diff --git a/libc/zoneinfo/zoneinfo.dat b/libc/zoneinfo/zoneinfo.dat
index bbea289..2e53be0 100644
--- a/libc/zoneinfo/zoneinfo.dat
+++ b/libc/zoneinfo/zoneinfo.dat
Binary files differ
diff --git a/libc/zoneinfo/zoneinfo.version b/libc/zoneinfo/zoneinfo.version
index 86d4eb7..10d350a 100644
--- a/libc/zoneinfo/zoneinfo.version
+++ b/libc/zoneinfo/zoneinfo.version
@@ -1 +1 @@
-2012a
+2012b