Fix Metasploit::Concern loading due to soft dependency on railties in gems

MSP-11359

# Verification Steps

## Specs
- [ ] `rake spec`
- [ ] VERIFY no failures`

## Cucumber
- [ ] `rake cucumber`
- [ ] VERIFY no failures

## `msfconsole`
- [ ] start msfconsole
- [ ] `creds add-password bob P@ssw0rd contosso`
- [ ] `creds`
- [ ] **VERIFY** output contains the password you just added