Guard against Bootstrap's max-width setting

Bootstrap sets both the max-width and max-height of all image elements to 100%.  When attributions are removed from their containing element, this causes logos to shrink.

css/ol.css

@@ -217,6 +217,7 @@ button.ol-full-screen-true:after {
 }
 .ol-attribution img {
   max-height: 2em;
+  max-width: inherit;
 }
 .ol-attribution ul, .ol-attribution button {
   display: inline-block;