fix(update): actually update the local file and not a global install

[MorganVonBrylan]

That's entirely my bad, I didn't properly pay attention while testing.
The update function actually tries to update the globally-installed yt-dlp and not one youtube-dl-exec downloaded. THe mistake lied in just two small characters... ./

[Kikobeats]

I promoted the change in this way:
af56495

wdyt?

[MorganVonBrylan]

The reason I had separated the working directory and the filename was so tinyspawn wouldn't crash if there is a space in the path, but I suppose fixing this issue here doesn't do much if it isn't also fixed in exec.