Clean up styling of Changelog dialog
Clean up styling of Changelog dialog

This prevents the button from being positioned on top of the scroll bar
and the horizontal scrollbar from showing.

Contributes to CURA-2519

Curahelper/Cura,ynotstartups/Wanhao,hmflash/Cura,fieldOfView/Cura,fieldOfView/Cura,Curahelper/Cura,hmflash/Cura,ynotstartups/Wanhao