Relative paths for buildifier still trigger warning on startup

[ryanwilsonperkin]

Follow up to #329

I'm now using v0.10.0 to take advantage of the ability to use a relative path for the buildifier executable, and while this does work for formatting, it still causes a warning on VSCode startup that the executable couldn't be found. I suspect that the warning check is still only looking at the system path, and isn't respecting the new relative path format.