Need to specified a pip version in dev Docker image

[Yancey1989]

Execute pip error after upgrade pip package to 10.0.0

[09:30:13] :	 [Step 1/1] Collecting pip
[09:30:13] :	 [Step 1/1]   Downloading pip-10.0.0-py2.py3-none-any.whl (1.3MB)
[09:30:13] :	 [Step 1/1] Installing collected packages: pip
[09:30:13] :	 [Step 1/1]   Found existing installation: pip 8.1.1
[09:30:13] :	 [Step 1/1]     Not uninstalling pip at /usr/lib/python2.7/dist-packages, outside environment /usr
[09:30:14] :	 [Step 1/1] Successfully installed pip-10.0.0
[09:30:14] :	 [Step 1/1]  [91mTraceback (most recent call last):
[09:30:14] :	 [Step 1/1]   File "/usr/bin/pip", line 9, in <module>
[09:30:14] :	 [Step 1/1]     from pip import main
[09:30:14] :	 [Step 1/1] ImportError: cannot import name main
[09:30:15]W:	 [Step 1/1] The command '/bin/sh -c pip install --upgrade pip &&     pip install -U wheel &&     pip install -U docopt PyYAML sphinx==1.5.6 &&     pip install sphinx-rtd-theme==0.1.9 recommonmark' returned a non-zero code: 1

[graycreate]

依然出错，请解决方法。

[Yancey1989]

看截图使用的依然是10.0.1版本的pip，重新build下dev镜像吧。

[graycreate]

知道为什么了，我是在构建android版，刚看到了这个6708546#diff-2af18a3bbc287c436f1750d66c034c98