Update the file handle upon each event
Update the file handle upon each event

Some text editors (vim, kate, etc) backup files on write.
The backup is done by renaming the original file and writing the
buffer to a new file with the original name.

This commit makes sure octodown reads the changes from the correct file.

Fixes ianks/octodown#90

ianks/octodown,ianks/octodown