Rakefile: run all targets by default
Rakefile: run all targets by default

This ensures that the entire build process, including the Rubocop
target, is exercised on each build.

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

bk2204/daniel-ruby,bk2204/daniel-ruby