fix script/local to work with .travis.yml changes

& raise an error when a version can’t be found
Throw error when gem adapters loaded w/out correct/any version

This won’t help #3128 since initializers are loaded before routes, but
it would’ve made the solution to #3131 clear.
update AA::Dependencies to use method_missing

so it can handle arbitrary gem names without having to be set up first
Dependencies -> Dependency