Broken python3.3 build on travis

[Mikhail Ushanov]

Error on installing boto requirements on python3.3:

Collecting cryptography>=1.5 (from paramiko>=1.10.0->-r requirements.txt (line 7))
 Downloading cryptography-2.1.1.tar.gz (441kB)
 100% |████████████████████████████████| 450kB 2.6MB/s
 Complete output from command python setup.py egg_info:
 error in cryptography setup command: Invalid environment marker: platform_python_implementation != 'PyPy'
 ----------------------------------------
Command "python setup.py egg_info" failed with error code 1 in /tmp/pip-build-cr_6nv/cryptography/
The command "pip install -r requirements.txt" failed. Retrying, 2 of 3.

Cause to paramiko and cryptography are dropped python3.3 support in latest releases.