treewide: Change URLs to HTTPS

Lots of URLs were HTTP redirect to HTTPS. Changed those and checked them
if there's actual content. Inspired by
https://github.com/NixOS/nixpkgs/issues/60004

pkgs/tools/text/diffstat/default.nix

@@ -18,7 +18,7 @@ stdenv.mkDerivation rec {
       insertions, deletions, and modifications per-file. It is useful for
       reviewing large, complex patch files.
     '';
-    homepage = http://invisible-island.net/diffstat/;
+    homepage = https://invisible-island.net/diffstat/;
     license = licenses.mit;
     platforms = platforms.unix;
     maintainers = [ maintainers.bjornfor ];

pkgs/tools/text/mawk/default.nix

@@ -13,7 +13,7 @@ stdenv.mkDerivation rec {
 
   meta = with stdenv.lib; {
     description = "Interpreter for the AWK Programming Language";
-    homepage = http://invisible-island.net/mawk/mawk.html;
+    homepage = https://invisible-island.net/mawk/mawk.html;
     license = licenses.gpl2;
     maintainers = with maintainers; [ ehmry ];
     platforms = with platforms; unix;

pkgs/tools/text/unoconv/unoconv-python3.patch

@@ -360,7 +360,7 @@ index 30e6706..f72cf08 100755
 -        print >>sys.stderr, "       http://github.com/dagwieers/unoconv/issues"
 +        print("unoconv: Cannot find a suitable office installation on your system.", file=sys.stderr)
 +        print("ERROR: Please locate your office installation and send your feedback to:", file=sys.stderr)
-+        print("       http://github.com/dagwieers/unoconv/issues", file=sys.stderr)
++        print("       https://github.com/dagwieers/unoconv/issues", file=sys.stderr)
          sys.exit(1)
  
      ### Now that we have found a working pyuno library, let's import some classes