Doc: fix typo in URL of OASIS group web site.

In other places that has been changed from http://www.oasis-open.org/
https://www.oasis-open.org/ but there's a place where the change was
missed.
Discussion: https://postgr.es/m/20190121.222844.399814306477973879.t-ishii%40sraoss.co.jp

diff --git a/doc/src/sgml/docguide.sgml b/doc/src/sgml/docguide.sgml
index 420a2f9d6e51fa036e784b415269a1606cf677e3..baa88b2fcef9ed0b139cc15659075dd9a182c025 100644 (file)
--- a/doc/src/sgml/docguide.sgml
+++ b/doc/src/sgml/docguide.sgml
@@ -80,7 +80,7 @@
 
    
     
-     DocBook DTD
+     s://www.oasis-open.org/docbook/">DocBook DTD
      
       
        This is the definition of DocBook itself.  We currently use version