remove git-modules
use local copy of bundler-audit.
coerce `resbody` to StringIO.
bootstrap the test environment.
add http/ruby-advisory-db as a git module.
add mpatch/bundler/audit/database.rb
remove Webaudit::Database.

sometime in the future it would be good to be re-introduce this class
but for now it is easier to use mpatch/bundler/audit/database.rb.
respond with 200 OK on success.