报错如下：
error: Microsoft Visual C++ 9.0 is required. Get it from http://aka.ms/vcpython27
解决方法：下载 VCForPython27.msi 。
地址： http://www.microsoft.com/en-us/download/confirmation.aspx?id=44266
(Microsoft Visual C++ Compiler for Python 2.7)
直接下载安装，安装完后重新pip install virtualenv
Successfully built virtualenv
Installing collected packages: wordcloud
Successfully installed wordcloud-1.3.1
成功！
error：Microsoft Visual C++ 9.0 is required. Get it
原文：http://blog.51cto.com/meyangyang/2094698