Fix frontend tests on Travis (PR #8089)

The only important change here is the distro update in Travis config (trusty to xenial).

This is required since the latest stable Chrome (77, released 2019-09-10) doesn’t support trusty, its installation attempt fails, and we try to run tests on a pre-installed version of Chrome (62, from 2017-10-17).

There are no side effects to that upgrade so far in my tests, but if there are any objections to this bump, we probably could install Chrome 76 (i.e. the last one that supported trusty) manually.

Note: This PR doesn’t fix the Travis build completely. Backend tests are failing too, see: DEV: Remove dreprecated review queue code by romanrizzi · Pull Request #47 · discourse/discourse-assign · GitHub


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fail looks unrelated to me!

undefined method `assign_locks_flags=’ for #Class:0x0000000006bd8840

 # ./plugins/discourse-assign/spec/integration/assign_spec.rb:77:in `bloc