Fix Travis CI build, add XCB build requirements, used in x11-clipboard#73

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timvisee wants to merge 2 commits intoaweinstock314:masterfrom timvisee:fix-travis-ci-xcb

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Commits on Feb 17, 2020

Fix Travis CI build, add XCB build requirements, used in x11-clipboard
timvisee
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Use Travis CI addons feature for installing apt packages
timvisee
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