Add upper bound for active-* gems

We do not yet support ActiveRecord and ActiveSupport 4.x, so ensure our Gemfile declares this.

Reported by @ZeroChaos

## Verification Steps

- [x] Run bundler: `bundle install`
- [x] Ensure `Gemfile.lock` does not change
- [x] Run `./msfconsole`
- [x] `db_status` shows database is connected