Install error on Python2.7

[mengzhuo]

System

$uname -a
Linux BJ-ZM-U 3.13.0-34-generic #60-Ubuntu SMP Wed Aug 13 15:45:27 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux
$pip --version
pip 1.5.5 from /home/meng/.virtualenvs/zty/local/lib/python2.7/site-packages (python 2.7)

Reproduce procedures:

pip install gunicorn
Downloading/unpacking gunicorn
  Using download cache from /home/meng/.pip/cache/https%3A%2F%2Fpypi.python.org%2Fpackages%2F2.7%2Fg%2Fgunicorn%2Fgunicorn-19.1.1-py2.py3-none-any.whl
Installing collected packages: gunicorn
Compiling /home/meng/.virtualenvs/zty/build/gunicorn/gunicorn/workers/_gaiohttp.py ...
  File "/home/meng/.virtualenvs/zty/build/gunicorn/gunicorn/workers/_gaiohttp.py", line 64
    yield from self.wsgi.close()
             ^
SyntaxError: invalid syntax

Successfully installed gunicorn
Cleaning up...

[wong2]

duplicate with #860