@Arnold @maurice_R @Phuket2 I fix this problem in Github.
The PyPi API was changed. The new link is 'https://pypi.org/pypi/{}/json'.
Thus, the simplest way to fix this is to find the pip.py (~/Modules/site-packages/stash/bin/pip.py) and change the old link(http://pypi.python.org/pypi/{}/json) to 'https://pypi.org/pypi/{}/json'