CLN: Added *.dta to the .gitignore. Fixed typo in comment. Removed import.
CLN: Removed import after flake8 said it wasn't needed.

3 trivialities I noticed while working on offsets.py.
 I think this just failed trivially...

`git --amend -C HEAD`

then force push again
 Seems to be failing due to a problem fetching data from yahoo. Not sure what to do about that. Run it again?
 go and push force push again...should be ok now
 thanks! 
