Update mc_parser.yy

Updated version requirements to indicate 3.0.  Will add #define or branch for <3.0 compatibility.

Author: jonathan-beard

mc_parser.yy

@@ -1,5 +1,5 @@
 %skeleton "lalr1.cc"
-%require  "2.7"
+%require  "3.0"
 %debug 
 %defines 
 %define api.namespace {MC}