Apply let/const transform.

_baseKeys.js

@@ -2,10 +2,10 @@ import isPrototype from './_isPrototype.js';
 import nativeKeys from './_nativeKeys.js';
 
 /** Used for built-in method references. */
-var objectProto = Object.prototype;
+const objectProto = Object.prototype;
 
 /** Used to check objects for own properties. */
-var hasOwnProperty = objectProto.hasOwnProperty;
+const hasOwnProperty = objectProto.hasOwnProperty;
 
 /**
  * The base implementation of `_.keys` which doesn't treat sparse arrays as dense.
@@ -18,8 +18,8 @@ function baseKeys(object) {
   if (!isPrototype(object)) {
     return nativeKeys(object);
   }
-  var result = [];
-  for (var key in Object(object)) {
+  const result = [];
+  for (const key in Object(object)) {
     if (hasOwnProperty.call(object, key) && key != 'constructor') {
       result.push(key);
     }