Step `I should see 'some string with "double" quotes'` should allow negation

[FLeinzi]

I recently found out that the single-quote step does not allow negations.

# Like `Then I should see`, but with single instead of double quotes. In case
# the expected string contains quotes as well.
Then /^(?:|I )should see '([^']*)'$/ do |text|
  patiently do
    expect(page).to have_content(text)
  end
end.overridable

This is a valid use case in my opinion, so I request a change here. I see no reason why we disallow the "not" here.