Blame doesn't update on out-of-atom file changes

[bblack]

1. Open a file in atom
2. ^B to open blame in the gutter
3. Edit the file outside of atom (e.g. do a git checkout to another version of the file)
4. Blame info doesn't change, but the visible file contents do, making the blame lines wrong

[alexcorre]

thanks for finding this...we should be able to be notified of when the contents change and update accordingly. i'll look into the docs and try to fix this.