Updated travis config
minor #465 Updated travis config (GrahamCampbell)

This PR was merged into the 5.1-dev branch.

Discussion
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Updated travis config

I've added phpunit 5.6 to the new travis.yml, and have added the verbose flag to phpunit. This flag means more details about skipped tests etc. are printed at the end.

Commits
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52a6a8d Updated travis config