update capistrano-foreman.gemspec for capistrano-bundler 2.2

currently capistrano-bundler is locked like this

```

  gem.add_dependency 'capistrano-bundler', '~> 1.1'
```

which prevent upgrading capistrano-bundler
and capistrano-bundler < 2 does not work with newer versions of bundler

could it be possible to update this ?