Bump to v4.2.1.

lodash.differenceby/index.js

@@ -1,5 +1,5 @@
 /**
- * lodash 4.2.0 (Custom Build) <https://lodash.com/>
+ * lodash 4.2.1 (Custom Build) <https://lodash.com/>
  * Build: `lodash modularize exports="npm" -o ./`
  * Copyright 2012-2016 The Dojo Foundation <http://dojofoundation.org/>
  * Based on Underscore.js 1.8.3 <http://underscorejs.org/LICENSE>
@@ -55,7 +55,8 @@ var getLength = baseProperty('length');
 /**
  * This method is like `_.difference` except that it accepts `iteratee` which
  * is invoked for each element of `array` and `values` to generate the criterion
- * by which uniqueness is computed. The iteratee is invoked with one argument: (value).
+ * by which they're compared. Result values are chosen from the first array.
+ * The iteratee is invoked with one argument: (value).
  *
  * @static
  * @memberOf _
@@ -126,8 +127,7 @@ function last(array) {
  * // => false
  */
 function isArrayLike(value) {
-  return value != null &&
-    !(typeof value == 'function' && isFunction(value)) && isLength(getLength(value));
+  return value != null && isLength(getLength(value)) && !isFunction(value);
 }
 
 /**
@@ -175,8 +175,8 @@ function isArrayLikeObject(value) {
  */
 function isFunction(value) {
   // The use of `Object#toString` avoids issues with the `typeof` operator
-  // in Safari 8 which returns 'object' for typed array constructors, and
-  // PhantomJS 1.9 which returns 'function' for `NodeList` instances.
+  // in Safari 8 which returns 'object' for typed array and weak map constructors,
+  // and PhantomJS 1.9 which returns 'function' for `NodeList` instances.
   var tag = isObject(value) ? objectToString.call(value) : '';
   return tag == funcTag || tag == genTag;
 }