quote the string

Author: ianfixes

lib/arduino_ci/display_manager.rb

@@ -82,7 +82,7 @@ def with_display
     def environment
       return nil unless @existing || @enabled
       return {} if @existing
-      { DISPLAY => ":1.0" }
+      { "DISPLAY" => ":1.0" }
     end
 
     # On finalize, ensure child process is ended