Default Flat Theme: Improve toolbar separator color

Make it the same as disabled icons, so that they are clearly different
from enabled icons.

Change-Id: I8b467745a91dc94cbf2db1cb9a83c927d90ce5c1
Reviewed-by: Alessandro Portale <alessandro.portale@theqtcompany.com>

share/qtcreator/themes/defaultflat.creatortheme

@@ -42,7 +42,7 @@ DoubleTabWidget2ndTabActiveTextColor=ffffffff
 DoubleTabWidget2ndTabBackgroundColor=ffff0000
 DoubleTabWidget2ndTabInactiveTextColor=ff000000
 EditorPlaceholderColor=ffdddddd
-FancyToolBarSeparatorColor=43ffffff
+FancyToolBarSeparatorColor=toolBarItemDisabled
 FancyTabBarBackgroundColor=shadowBackground
 FancyTabWidgetDisabledSelectedTextColor=toolBarItemDisabled
 FancyTabWidgetDisabledUnselectedTextColor=toolBarItemDisabled