Fix mistake in README section for Grammar

Author: h0tk3y

README.md

@@ -219,7 +219,7 @@ interface Item
 class Number(val value: Int) : Item
 class Variable(val name: String) : Item
 
-object ItemsParser : Grammar<Item>() {
+object ItemsParser : Grammar<List<Item>>() {
     val num by token("\\d+")
     val word by token("[A-Za-z]")
     val comma by token(",\\s+")