configure.ac: fix typo from 3ef3ba4d2
diff --git a/configure.ac b/configure.ac
index e526d17..2d31273 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1,4 +1,4 @@
-nl Process this file with autoconf to create configure.
+dnl Process this file with autoconf to create configure.
 
 AC_PREREQ([2.59])