deliberate ES6 syntax

(rationale: don't let people install @2 in a build system that will not alert them that we have moved to ES6, only to cause trouble with a later release.)

src/constant.js

@@ -1,5 +1 @@
-export default function(x) {
-  return function() {
-    return x;
-  };
-}
+export default x => () => x;