Login: adjust login width decimal place

see #1475

app/assets/stylesheets/zammad.scss

@@ -2336,7 +2336,7 @@ kbd {
   }
 
   .btn:not(.btn--text) {
-    min-width: calc(33% - 6px); // auth provider width
+    min-width: calc(33.33% - 6px); // auth provider width
   }
 }