add English "year" translation

src/defaults.js

@@ -42,6 +42,7 @@ Calendar.defaults = {
 		next: "next",
 		prevYear: "prev year",
 		nextYear: "next year",
+		year: 'year', // TODO: locale files need to specify this
 		today: 'today',
 		month: 'month',
 		week: 'week',