RuntimeError crash when a table is not well formatted

[thinkingerrol]

Feature: Table formatting

  As a developer,
  I want clear output from gherkin_format, without misleading errors.

  Scenario: Misformatted table
    Given a scenario has a mis-formatted table
      | title  |
      | content |     
    When I run gherkin_format
    Then I don't get a RuntimeError

$ docker run --rm -i -v $(pwd):/src -w /src gherkin/format:0.1.1 test/table.feature
/usr/local/bundle/gems/gherkin_format-0.1.1/lib/gherkin_format.rb:28:in `format': File test/table.feature is not formatted well. (RuntimeError)
        from /usr/local/bundle/gems/gherkin_format-0.1.1/bin/gherkin_format:40:in `block in <top (required)>'
        from /usr/local/bundle/gems/gherkin_format-0.1.1/bin/gherkin_format:39:in `each'
        from /usr/local/bundle/gems/gherkin_format-0.1.1/bin/gherkin_format:39:in `<top (required)>'
        from /usr/local/bundle/bin/gherkin_format:22:in `load'
        from /usr/local/bundle/bin/gherkin_format:22:in `<main>'
File test/table.feature is not formatted well.

Despite the RuntimeError, gherkin_format seems to do the job, at least with -replace is fixes the mis-formatted table. Unfortunately, it does not say that it replaced anything and especially with the RuntimeError it looks like the input was so bad that gherkin_format couldn't do it's job and crashed.

Please fix the RuntimeError and also write out an indication that a file has been changed automatically.