Travis running python 3.7 for testing but showing 3.4 on darwin(xcode/macos) build

The link to the build is https://travis-ci.org/zulip/zulip-terminal/builds/469486791?utm_source=github_status&utm_medium=notification

Travis is running tests on python 3.7 but ENV is set to be 3.4.

What ENV are you talking about? Your Mac job https://travis-ci.org/zulip/zulip-terminal/jobs/469486796 is using language: generic, so I am a bit surprised that anything is set to 3.4.