Rakefile: avoid rebuilding JS files needlessly.
Rakefile: avoid rebuilding JS files needlessly.

Structure the targets more based on file dependencies, which rake can
automatically determine are up-to-date.

Signed-off-by: brian m. carlson <738bdd359be778fee9f0fc4e2934ad72f436ceda@crustytoothpaste.net>

bk2204/daniel-ruby,bk2204/daniel-ruby