Could not fetch URL https://pypi.python.org/simple/beautifulsoup4/: There was a problem confirming the ssl certificate: [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:645) - skipping
安装 beautifulsoup4，报错：
Could not fetch URL https://pypi.python.org/simple/beautifulsoup4/: There was a problem confirming the ssl certificate: [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:645) - skipping
