Fix requirements.txt (again)

[zmousm]

• No need to bump PyYAML min. version to 3.11 (Debian Wheezy provides 3.10 and that should still work).
• The less than next "release" notation for max. version has the unfortunate side effect that a pre-release version apparently passes this spec. So fix the spec for Django to ensure that pip will not install anything later than 1.8.x.

  >>> from pkg_resources import parse_version
  >>> parse_version('1.9c1') < parse_version('1.9')
  True

While:

  >>> parse_version('1.9c1') < parse_version('1.9a')
  False

See: http://stackoverflow.com/questions/11887762/compare-version-strings/21065570#21065570 https://setuptools.readthedocs.io/en/latest/setuptools.html#specifying-your-project-s-version

[zmousm]

@vladimir-mencl-eresearch fyi

[vladimir-mencl-eresearch]

Thanks - I did not run into any issues with a 1.9a version slipping in, but it's looking good to me.

Cheers, Vlad