Steps to reproduce

Go to: https://travis-ci.org/PowerShell/PowerShell. The xcode tag is set on both the Ubuntu Trusty and macOS job because the osx_image setting is defined globally instead of in a matrix as recommended here.

Expected behavior

The xcode tag should not be set for Ubuntu Trusty Travis CI jobs.

Actual behavior

The xcode tag is set for Ubuntu Trusty Travis CI jobs. Example: https://travis-ci.org/PowerShell/PowerShell/builds/307043228

Environment data

N/A