db_text: spelling fix withing -> within

src/modules/db_text/doc/db_text.cfg

@@ -76,7 +76,7 @@ route{
     # use different transport protocol
     if (!method=="REGISTER") record_route();
 
-    # subsequent messages withing a dialog should take the
+    # subsequent messages within a dialog should take the
     # path determined by record-routing
     if (loose_route()) {
         # mark routing logic in request