How to simulate keyboard events in Capybara and Poltergeist
```ruby
Then(/^when I press backspace in '(.*?)'$/) do |input|
focus_field(input)
find_field(input).native.send_keys(:Backspace)
end
```
Details:
https://github.com/teampoltergeist/poltergeist/blob/master/spec/integration/driver_spec.rb#L1203