`gdk_monitor_get_scale_factor: assertion 'GDK_IS_MONITOR (monitor)' failed` on Windows

[timholy]

This is a message that appears on Windows Travis tests (I haven't tested locally). While they don't seem to cause a problem, the sheer number of such warnings makes it hard to read the logs: https://travis-ci.org/JuliaGizmos/GtkReactive.jl/jobs/622293711?utm_medium=notification&utm_source=github_status

FYI this is not new; it also happens on the pre-JLL packages, e.g., https://travis-ci.org/JuliaGizmos/GtkReactive.jl/jobs/622293711?utm_medium=notification&utm_source=github_status