在安装vatic时，试图设置virtualenv出错“不能导入名称_remove_dead_weakref”。

Im trying to install vatic, and one requirement is to run 'virtualenv .env' from the vatic workspace. When I run this, I get that ~/anaconda2/lib/python2.7/weakref.py has an error 'cannot import name_remove_dead_weakref.Im trying to install vatic, and one requirement