Exclude YARD templates directory from yard doc

The templates directory is full of stuff that `yard doc` can't process. This
causes a bunch of ugly warnings to flash across the screen.
Monkeypatch a fix into YARD::Logger#show_progress

This method has an inverted conditional which means the progress bar still
animates when `--debug` is passed. Not having an easy way to switch the
animation off is a real bummer as it completely hoses the Pry REPL.

Ref. lsegal/yard#783