Update other man pages to match leap second reality

Missed these in r334501; see justification there:

https://svnweb.freebsd.org/base?view=revision&revision=334501

Sponsored by:	Dell EMC Isilon

bin/date/date.1

@@ -32,7 +32,7 @@
 .\"     @(#)date.1	8.3 (Berkeley) 4/28/95
 .\" $FreeBSD$
 .\"
-.Dd May 7, 2015
+.Dd June 1, 2018
 .Dt DATE 1
 .Os
 .Sh NAME
@@ -296,8 +296,8 @@ Hour, a number from 0 to 23.
 .It Ar MM
 Minutes, a number from 0 to 59.
 .It Ar ss
-Seconds, a number from 0 to 61
-(59 plus a maximum of two leap seconds).
+Seconds, a number from 0 to 60
+(59 plus a potential leap second).
 .El
 .Pp
 Everything but the minutes is optional.

usr.bin/at/at.man

@@ -294,7 +294,7 @@ The hour of the day, from 0 to 23.
 .It Ar mm
 The minute of the hour, from 0 to 59.
 .It Ar SS
-The second of the minute, from 0 to 61.
+The second of the minute, from 0 to 60.
 .El
 .Pp
 If the

usr.bin/last/last.1

@@ -28,7 +28,7 @@
 .\"     @(#)last.1	8.1 (Berkeley) 6/6/93
 .\" $FreeBSD$
 .\"
-.Dd June 6, 2015
+.Dd June 1, 2018
 .Dt LAST 1
 .Os
 .Sh NAME
@@ -121,7 +121,7 @@ Hour of the day, from 0 to 23.
 .It Ar mm
 Minute of the hour, from 0 to 59.
 .It Ar SS
-Second of the minute, from 0 to 61.
+Second of the minute, from 0 to 60.
 .El
 .Pp
 If the