explicitly drop Yacc, Bison < 3 compatibility in exparse.y

Yacc was already not supported as this parser is using Bison extensions, but
this at least makes explicit what our requirements are. This is the equivalent
of 4a13c9598ad3d950a251e5d3e5be8d05c59c6214. Related to #1806.

diff --git a/lib/expr/exparse.y b/lib/expr/exparse.y
index 5cf530e830e721fe836c4e618d40d5ad00017319..cb150ed7ad859fdfaa6a4d43a36eb379a17efe72 100644 (file)
--- a/lib/expr/exparse.y
+++ b/lib/expr/exparse.y
@@ -11,6 +11,8 @@
  * Contributors: See CVS logs. Details at http://www.graphviz.org/
  *************************************************************************/
 
+%require "3.0"
+
 %{
 
 /*