Installer (and thus travis tests) broken with python3.3

[tedivm]

It looks like cryptography is no longer supporting python 3.3, which in turn breaks this project's continuous integration setup.

Collecting cryptography (from Beaker==1.9.0)
  Downloading cryptography-2.1.4.tar.gz (441kB)
    100% |████████████████████████████████| 450kB 3.5MB/s 
    Complete output from command python setup.py egg_info:
    error in cryptography setup command: Invalid environment marker: platform_python_implementation != 'PyPy'

[amol-]

Added constraint on cryptography for python 3.3, built now passing https://travis-ci.org/bbangert/beaker/builds/312098632

Note btw that the issue is probably more related to the pip version than to the python version, but as we are talking about a test dependency I think it's reasonable to constraint on py3.3 for versions that were able to install