Support '# noqa' on future import line

Normally with flake8 I could add something like ` # noqa: FI14` to a line to get flake8 to ignore an error.

For the future imports checking, it seems like the only way this is respected is if it is on the very first line of a file. However, this is impractical if you have a script with a shebang line. I would like to add it to the `from __future__ import` line. 
