Ensure stack is popped after recursive merge so that it doesn't affect sibling properties. [closes #2060]

lodash.js

@@ -3209,6 +3209,7 @@
         // Recursively merge objects and arrays (susceptible to call stack limits).
         mergeFunc(newValue, srcValue, srcIndex, customizer, stack);
       }
+      stack['delete'](srcValue);
       assignMergeValue(object, key, newValue);
     }