Make it so prism can print out its AST in 'ast'

Author: enebo

bin/ast

@@ -158,7 +158,7 @@ if options[:print_ast]
     DotGraph.print_graph(root)
   else
     print "AST:"
-    puts indent(root.to_string) 
+    puts indent(root.get_ast.to_string) 
     puts
   end
 end