Set viewport width to device width

[tim-yao]

🤔 What's changed?

Add the HTML's viewport meta tag to support mobile view.
See https://developer.mozilla.org/en-US/docs/Learn/CSS/CSS_layout/Responsive_Design#the_viewport_meta_tag

Before:

After:

⚡️ What's your motivation?

Fixes: #237

🏷️ What kind of change is this?

• ⚡ New feature (non-breaking change which adds new behaviour)

♻️ Anything particular you want feedback on?

Not sure how to visually test it. But I add this line to my generated report does the job.

📋 Checklist:

• I agree to respect and uphold the Cucumber Community Code of Conduct
• I've changed the behaviour of the code
  • I have added/updated tests to cover my changes.
• My change requires a change to the documentation.
  • I have updated the documentation accordingly.
• Users should know about my change
  • I have added an entry to the "Unreleased" section of the CHANGELOG, linking to this pull request.

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[mpkorstanje]

Cheers. Released in v20.3.1. If you aren't using Cucumber-JVM you may have to poke some of the maintainers for a release.