Make railites a hard dep

MSP-11359

# Pre-verification Steps

- [x] Release rapid7/metasploit-model#24
- [x] Release rapid7/metasploit-concern#8
- [x] Update `metasploit_data_models.gemspec` to use released versions

# Verification Steps

## Specs
- [x] `rake spec`
- [x] VERIFY no failures

# Post-merge Steps

Perform these steps prior to pushing to master or the build will be broke on master.

## Version
- [x] Edit `lib/metasploit/model/version.rb`
- [x] Remove `PRERELEASE` and its comment as `PRERELEASE` is not defined on master.

## Gem build
- [x] gem build *.gemspec
- [x] VERIFY the gem has no '.pre' version suffix.

## RSpec
- [ ] `rake spec`
- [ ] VERIFY version examples pass without failures

## Commit & Push
- [ ] `git commit -a`
- [ ] `git push origin master`

# Release

## JRuby
- [ ] `rvm use jruby@metasploit_data_models`
- [ ] `rm Gemfile.lock`
- [ ] `bundle install`
- [ ] `rake release`

## MRI Ruby
- [ ] `rvm use ruby-1.9.3@metasploit_data_models`
- [ ] `rm Gemfile.lock`
- [ ] `bundle install`
- [ ] `rake release`