Replaced a tab with 4 spaces, as in all the other lines

Author: Dr4K4n

data/meld.css

@@ -1,6 +1,6 @@
 
 .meld-notebook-toolbar {
-	background-image: none;
+    background-image: none;
     background-color: @theme_bg_color;
     border-width: 0 0 1px 0;
     border-style: solid;