Update the POSIX Extended section of the Regular Expression Wikipedia page

PiperOrigin-RevId: 479667644
Change-Id: I4ab03bd5f0520f8586667de8bd1b9443f241337a

docs/advanced.md

@@ -487,7 +487,7 @@ When built with Bazel and using Abseil, googletest uses the
 systems (Linux, Cygwin, Mac), googletest uses the
 [POSIX extended regular expression](http://www.opengroup.org/onlinepubs/009695399/basedefs/xbd_chap09.html#tag_09_04)
 syntax. To learn about POSIX syntax, you may want to read this
-[Wikipedia entry](http://en.wikipedia.org/wiki/Regular_expression#POSIX_Extended_Regular_Expressions).
+[Wikipedia entry](http://en.wikipedia.org/wiki/Regular_expression#POSIX_extended).
 
 On Windows, googletest uses its own simple regular expression implementation. It
 lacks many features. For example, we don't support union (`"x|y"`), grouping