Disable display manager to see if CI still fails (or if Arduino removed the GUI)

Author: ianfixes

lib/arduino_ci/display_manager.rb

@@ -33,11 +33,7 @@ def initialize
     # attempt to determine if the machine is running a graphical display (i.e. not Travis)
     # @return [bool] whether there is already a GUI that can accept windows
     def existing_display?
-      return true  if RUBY_PLATFORM.include? "darwin"
-      return true  if Host.os == :windows
-      return false if ENV["DISPLAY"].nil?
-      return true  if ENV["DISPLAY"].include? ":"
-      false
+      true
     end
 
     # check whether a process is alive