[gtk-doc] configure: bump perl dependency

[Stefan Kost <stefkost src gnome org>]

commit ea7536e70f783cdd04809d68e04ba07bb754693e
Author: Stefan Sauer <ensonic users sf net>
Date:   Thu Oct 15 21:46:21 2015 +0200

    configure: bump perl dependency
    
    We need a newer perl for the '?R' support in regex.
    Fixes #756519

 configure.ac |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 1e092af..02e323a 100644
--- a/configure.ac
+++ b/configure.ac
@@ -39,12 +39,12 @@ if test -z "$PERL"; then
        AC_MSG_ERROR([perl not found])
 fi
 
-AC_MSG_CHECKING([if Perl version >= 5.6.0])
-if "$PERL" -e "require v5.6.0"; then
+AC_MSG_CHECKING([if Perl version >= 5.18.0])
+if "$PERL" -e "require v5.18.0"; then
        AC_MSG_RESULT([yes])
 else
        AC_MSG_RESULT([no])
-       AC_MSG_ERROR([perl >= 5.6.0 is required for gtk-doc])
+       AC_MSG_ERROR([perl >= 5.18.0 is required for gtk-doc])
 fi
 
 dnl