Fix css property name (#208)

Author: Siborgium

bar/style.css

@@ -14,7 +14,7 @@ button {
     padding-left: 10px;
     padding-right: 10px;
     margin: 5px;
-    -gtk-icon-style: none;
+    -gtk-icon-shadow: none;
 }
 
 button:hover {