Re-enable pry command

The switch to bundler broke pry. This change, along with starting
msfconsole with a command like: `ruby -r pry ./msfconsole`, makes using
it possible again.

## Verification

- [x] gem install pry
- [x] start msfconsole with `ruby -r pry ./msfconsole`
- [x] use a module
- [x] type `pry`
- [x] verify working pry console