Fix travis build

[mbaumgartl]

Travis changed the way they handle xvfb. I also updated Node.js LTS versions.

[googlebot]

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[mbaumgartl]

@googlebot I signed it!

[googlebot]

We found a Contributor License Agreement for you (the sender of this pull request), but were unable to find agreements for all the commit author(s) or Co-authors. If you authored these, maybe you used a different email address in the git commits than was used to sign the CLA (login here to double check)? If these were authored by someone else, then they will need to sign a CLA as well, and confirm that they're okay with these being contributed to Google.
In order to pass this check, please resolve this problem and then comment @googlebot I fixed it.. If the bot doesn't comment, it means it doesn't think anything has changed.

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[mbaumgartl]

@googlebot I fixed it.

[googlebot]

CLAs look good, thanks!

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[johnjbarton]

Please separate these commits into two PRs so they are merged separately.

Please add
BREAKING CHANGE: drop support for node 8
to this commit description.

[mbaumgartl]

I removed the version commit from the PR but I'm not sure if correctly created the new pull request (#215). If not, I created it from master after #213 was merged.

[johnjbarton]

Thanks!

[karmarunnerbot]

🎉 This PR is included in version 2.0.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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