Update doc examples to ES2015.

at.js

@@ -10,7 +10,7 @@ import baseAt from './.internal/baseAt.js';
  * @returns {Array} Returns the picked values.
  * @example
  *
- * var object = { 'a': [{ 'b': { 'c': 3 } }, 4] };
+ * const object = { 'a': [{ 'b': { 'c': 3 } }, 4] };
  *
  * at(object, ['a[0].b.c', 'a[1]']);
  * // => [3, 4]