Fix build per microsoft/vscode#75873

[octref]

Fix Linux build on Travis. See microsoft/vscode#75873.

[jpoon]

Oh snap, didn't see this PR. Made the same change. Thanks @octref

[octref]

@jpoon Your change won't work as multi-line scripts need to have |:

before_install:
- |
  if...
    ...
  fi

[octref]

And I have tested, /usr/bin/Xvfb :99 -screen 0 1024x768x24 > /dev/null 2>&1 & with semicolon in the end would cause a syntax error. Maybe you can use (/usr/bin/Xvfb :99 -screen 0 1024x768x24 > /dev/null 2>&1 &);.

Before this commit my build failed as well: octref/vscode-test-sample@0787a54

[jpoon]

Reverted my commit and will just take yours as soon as this builds.