title: Install scrapy on mac successful, but run error
body: <pre><code>gaoyaqiu:git gaoyaqiu$ scrapy 
  Traceback (most recent call last):
    File /usr/local/bin/scrapy, line 7, in &lt;module&gt;
        from scrapy.cmdline import execute
    File /Library/Python/2.7/site-packages/scrapy/cmdline.py, line 9, in &lt;module&gt;
        from scrapy.crawler import CrawlerProcess
    File /Library/Python/2.7/site-packages/scrapy/crawler.py, line 7, in &lt;module&gt;
        from twisted.internet import reactor, defer
    File /Library/Python/2.7/site-packages/twisted/internet/reactor.py, line 38, in &lt;module&gt;
        from twisted.internet import default
    File /Library/Python/2.7/site-packages/twisted/internet/default.py, line 56, in &lt;module&gt;
        install = _getInstallFunction(platform)
    File /Library/Python/2.7/site-packages/twisted/internet/default.py, line 50, in _getInstallFunction
        from twisted.internet.selectreactor import install
    File /Library/Python/2.7/site-packages/twisted/internet/selectreactor.py, line 18, in &lt;module&gt;
        from twisted.internet import posixbase
    File /Library/Python/2.7/site-packages/twisted/internet/posixbase.py, line 18, in &lt;module&gt;
        from twisted.internet import error, udp, tcp
    File /Library/Python/2.7/site-packages/twisted/internet/tcp.py, line 28, in &lt;module&gt;
        from twisted.internet._newtls import (
    File /Library/Python/2.7/site-packages/twisted/internet/_newtls.py, line 21,  in &lt;module&gt;
        from twisted.protocols.tls import TLSMemoryBIOFactory, TLSMemoryBIOProtocol
    File /Library/Python/2.7/site-packages/twisted/protocols/tls.py, line 63, in  &lt;module&gt;
        from twisted.internet._sslverify import _setAcceptableProtocols
    File /Library/Python/2.7/site-packages/twisted/internet/_sslverify.py, line 38, in &lt;module&gt;
        TLSVersion.TLSv1_1: SSL.OP_NO_TLSv1_1,
  AttributeError: module object has no attribute OP_NO_TLSv1_1
  </code></pre>