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

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