doc: update links to current pages

It's somewhat traditional to respect sites' self-identification.

Signed-off-by: Josh Soref <jsoref@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Cherry-picked-from: 65175d9
Signed-off-by: Johannes Sixt <j6t@kdbg.org>

Author: jsoref

gitk

@@ -12472,7 +12472,7 @@ if {[tk windowingsystem] eq "aqua"} {
 
 catch {
     # follow the XDG base directory specification by default. See
-    # http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html
+    # https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html
     if {[info exists env(XDG_CONFIG_HOME)] && $env(XDG_CONFIG_HOME) ne ""} {
         # XDG_CONFIG_HOME environment variable is set
         set config_file [file join $env(XDG_CONFIG_HOME) git gitk]