Msftidy: use binary on File.open always

msftidy is complaining, here:

keylog_recorder.rb:116 - [WARNING] File.open without binary mode

Not sure how this managed to hit upstream/master with msftidy warnings.
Protip, use an msftidy pre-commit hook. We have just such a hook script
in tools/dev, as a matter of fact, so it's just a symlink away:

https://github.com/rapid7/metasploit-framework/blob/master/tools/dev/pre-commit-hook.rb