minor #160 add php 7.3 to travis (andreybolonin)
minor #160 add php 7.3 to travis (andreybolonin)

This PR was merged into the 1.9-dev branch.

Discussion
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add php 7.3 to travis

Commits
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79ad4a0 Update .travis.yml

nicolas-grekas/polyfill,symfony/polyfill