Change to https for tigervnc URL

Our main web site now supports https, so update all references.
diff --git a/unix/x0vncserver/x0vncserver.man b/unix/x0vncserver/x0vncserver.man
index 5dc0b05..5f1508c 100644
--- a/unix/x0vncserver/x0vncserver.man
+++ b/unix/x0vncserver/x0vncserver.man
@@ -302,7 +302,7 @@
 .BR Xvnc (1),
 .BR vncpasswd (1),
 .br
-http://www.tigervnc.org/
+https://www.tigervnc.org/
 
 .SH AUTHOR
 Constantin Kaplinsky and others.