Ensure callback shorthands work with _.uniq. [\ht @jden, @motowilliams]

Former-commit-id: d9a0e688414edc4167b5f8e9ca123bab587f8264

lodash.js

@@ -3950,7 +3950,7 @@
           seen = result;
 
       // juggle arguments
-      if (typeof isSorted == 'function') {
+      if (typeof isSorted != 'boolean' && isSorted != null) {
         thisArg = callback;
         callback = isSorted;
         isSorted = false;
@@ -3960,7 +3960,7 @@
       if (isLarge) {
         var cache = {};
       }
-      if (callback) {
+      if (callback != null) {
         seen = [];
         callback = createCallback(callback, thisArg);
       }