Update TODO

Add entry for the `download.txt` filename bug.
Fix downloaded filename 'download.txt' bug

As of Chrome 35, the downloaded file would appear with the filename
'download.txt' instead of the custom defined timestamped filename. Use a
JS blob instead of a data URL to download the file so that the filename
sticks.
TODO: update, fix for 'download.txt' filename bug
Merge branch 'filename-incorrect-on-chrome-35'