Fix typo from previous commit

Author: khurshid-alam

gtk-3.0/scss/widgets/_infobar.scss

@@ -28,7 +28,7 @@
             border: 1px solid shade($bg_color, .8);
             color: $fg_color;
 
-            button {
+            .button {
                 @include button($bg_color, $fg_color);
 
                 &.close { @extend %close_button; }