drop compatibility with Yacc, Bison < 3 in lib/cgraph/grammar.y

This will allow us to use api.prefix with brace syntax in an upcoming commit.
Bison 3.0 was released in July 2013 [0], so this seems an acceptable base line
requirement from now on.

  [0]: http://savannah.gnu.org/forum/forum.php?forum_id=7663

diff --git a/lib/cgraph/grammar.y b/lib/cgraph/grammar.y
index c089677208fe3f5a6fb8be01146dfde6f8e6f926..737b147fecabf74c50b30a0bc846bcf4dfadfda3 100644 (file)
--- a/lib/cgraph/grammar.y
+++ b/lib/cgraph/grammar.y
@@ -11,6 +11,8 @@
  * Contributors: See CVS logs. Details at http://www.graphviz.org/
  *************************************************************************/
 
+%require "3.0"
+
 %{
 
 #include <stdio.h>  /* SAFE */