Use absolute import

Only skip absolute imports when the only import is a __future__
statement.

Closes #59
Bump the priority of fix_import

Guarantees it does its thing before any other fixer accidentally blocks
its execution.
Merge pull request #77 from brettcannon/future_import

Use absolute import
Merge remote-tracking branch 'upstream/master' into simplification
Skip six imports for map and filter when changed to a list comp