move transformers over to using ast-types when constructing new nodes

lib/6to5/transformers/rest-parameters.js

@@ -1,5 +1,7 @@
 var util = require("../util");
+var b    = require("ast-types").builders;
 
+exports.FunctionDeclaration =
 exports.FunctionExpression = function (node) {
   if (!node.rest) return;
 
@@ -11,9 +13,6 @@ exports.FunctionExpression = function (node) {
 
   node.body.body.unshift(util.template(templateName, {
     VARIABLE_NAME: rest,
-    SLICE_ARG: {
-      type: "Literal",
-      value: node.params.length
-    }
+    SLICE_ARG: b.literal(node.params.length)
   }));
 };