gnu: Use HTTPS for invisible-island.net home pages.

* gnu/packages/ncurses.scm (dialog)[home-page]: Use HTTPS.
* gnu/packages/version-control.scm (diffstat)[home-page]: Likewise.
* gnu/packages/xorg.scm (xterm)[home-page]: Likewise.

gnu/packages/ncurses.scm

@@ -224,7 +224,7 @@ ncursesw library provides wide character support.")
     (synopsis "Curses widgets")
     (description "Dialog is a script-interpreter which provides a set of
 curses widgets, such as dialog boxes.")
-    (home-page "http://invisible-island.net/dialog/dialog.html")
+    (home-page "https://invisible-island.net/dialog/dialog.html")
     ;; Includes the gpl3 file "config.sub" from Automake.
     (license (list lgpl2.1 gpl3))))
 

gnu/packages/version-control.scm

@@ -1183,7 +1183,7 @@ standards-compliant ChangeLog entries based on the changes that it detects.")
                (base32
                 "1vjmda2zfjxg0qkaj8hfqa8g6bfwnn1ja8696rxrjgqq4w69wd95"))))
     (build-system gnu-build-system)
-    (home-page "http://invisible-island.net/diffstat/")
+    (home-page "https://invisible-island.net/diffstat/")
     (synopsis "Make histograms from the output of @command{diff}")
     (description
      "Diffstat reads the output of @command{diff} and displays a histogram of

gnu/packages/xorg.scm

@@ -5813,7 +5813,7 @@ to answer a question.  Xmessage can also exit after a specified time.")
        ("libXt" ,libxt)
        ("xproto" ,xproto)
        ("libXaw" ,libxaw)))
-    (home-page "http://invisible-island.net/xterm/")
+    (home-page "https://invisible-island.net/xterm/")
     (synopsis "Terminal emulator for the X Window System")
     (description
      "The xterm program is a terminal emulator for the X Window System.  It