Allow _.zipObject to accept an array of keys without assuming its an array of key/value pairs. [closes #397]

dist/lodash.underscore.js

@@ -3589,6 +3589,9 @@
         length = keys ? keys.length : 0,
         result = {};
 
+    if (!values && length && !isArray(keys[0])) {
+      values = [];
+    }
     while (++index < length) {
       var key = keys[index];
       if (values) {