bumped python-magic to 0.4.6 to solve no magic files loaded

magic.MagicException: no magic files loaded

for more info please have a look at
https://github.com/ahupp/python-magic/issues/44
use module functions instead of Magic class

It will solve following:

Exception: attempting to use libmagic on multiple threads will end in
SEGV.  Prefer to use the module functions from_file or from_buffer, or
carefully manage direct use of the Magic class
Merge pull request #963 from everplays/broken-python-magic

Broken python-magic