Point at correct manual

Index: man/vis.1
--- man/vis.1.orig
+++ man/vis.1
@@ -260,7 +260,7 @@ currently defers regular expression matching to the un
 It uses what POSIX refers to as
 .Dq Extended Regular Expressions
 as described in
-.Xr regex 7 .
+.Xr re_format 7 .
 The anchors
 .Ic ^
 and