Make _.where iterate over only own properties.

Former-commit-id: 29b4cafe5271cad70c711c2d401cea627fa97e33

lodash.js

@@ -2537,10 +2537,7 @@
    * // => [{ 'name': 'moe', 'age': 40 }]
    */
   function where(collection, properties) {
-    var props = [];
-    forIn(properties, function(value, prop) {
-      props.push(prop);
-    });
+    var props = keys(properties);
     return filter(collection, function(object) {
       var length = props.length;
       while (length--) {