fix AC_CONFIG_AUX_DIR typo

in b39fe4c1 another AC_CONFIG_AUX_DIR macro was added, this was supposed
to be AC_CONFIG_MACRO_DIR, this fixes this.

configure.ac

@@ -9,7 +9,7 @@ AC_COPYRIGHT([Copyright (C) 2008 Kipp C. Cannon])
 # top-level directory of the source tree
 AC_CONFIG_SRCDIR([gnuscripts/ltmain.sh])
 AC_CONFIG_AUX_DIR([gnuscripts])
-AC_CONFIG_AUX_DIR([gnuscripts])
+AC_CONFIG_MACRO_DIR([gnuscripts])
 AM_INIT_AUTOMAKE([foreign])
 AC_CONFIG_FILES([ \
 	Makefile \