youtube-dl: update to 2014.11.4

with slight tweak of caveat's format.
Current caveats look like this:
```
==> Caveats
To use post-processing options, `brew install ffmpeg`.
Bash completion has been installed to:
  /usr/local/etc/bash_completion.d

zsh completion has been installed to:
  /usr/local/share/zsh/site-functions
```

You see, missing an "\n".