Ensure _.find returns undefinedwhen a value cannot be found. [closes #15]

Former-commit-id: e6dc89f98a1df81e1b1d67c5e8f5725e4df3bc5a

lodash.js

@@ -585,6 +585,7 @@
    * // => 2
    */
   var find = createIterator(baseIteratorOptions, {
+    'init': '',
     'inLoop': 'if (callback(collection[index], index, collection)) return collection[index]'
   });