Without requiring `action_view` the following occurs:
```bash
(bundle-console)$ bundle console                                                                                                                                                                                                                                              
Resolving dependencies...
Unfortunately, a fatal error has occurred. Please see the Bundler 
troubleshooting documentation at http://bit.ly/bundler-issues. Thanks! 
/Users/gert/Projects/self/var/griddler/lib/griddler/email.rb:4:in `<class:Email>': uninitialized constant Griddler::Email::ActionView (NameError)
        from /Users/gert/Projects/self/var/griddler/lib/griddler/email.rb:3:in `<top (required)>'
        from /Users/gert/Projects/self/var/griddler/lib/griddler.rb:5:in `require'
        from /Users/gert/Projects/self/var/griddler/lib/griddler.rb:5:in `<top (required)>'
```

Without requiring `rails` the following occurs:
```bash
(bundle-console)$ bundle console
Resolving dependencies...
Unfortunately, a fatal error has occurred. Please see the Bundler 
troubleshooting documentation at http://bit.ly/bundler-issues. Thanks! 
/Users/gert/Projects/self/var/griddler/lib/griddler/engine.rb:2:in `<module:Griddler>': uninitialized constant Rails (NameError)
        from /Users/gert/Projects/self/var/griddler/lib/griddler/engine.rb:1:in `<top (required)>'
        from /Users/gert/Projects/self/var/griddler/lib/griddler.rb:4:in `require'
        from /Users/gert/Projects/self/var/griddler/lib/griddler.rb:4:in `<top (required)>'

```

Is seems that requiring `rails/engine` would solve this as well. I will update the pull-request.