Apply even more let/const transforms.

defaultsDeep.js

@@ -22,7 +22,7 @@ import mergeWith from './mergeWith.js';
  * _.defaultsDeep({ 'a': { 'b': 2 } }, { 'a': { 'b': 1, 'c': 3 } });
  * // => { 'a': { 'b': 2, 'c': 3 } }
  */
-var defaultsDeep = baseRest(args => {
+const defaultsDeep = baseRest(args => {
   args.push(undefined, customDefaultsMerge);
   return apply(mergeWith, undefined, args);
 });