Update search to lower case as well

This will covert the search text to lower case as well for usability.

packages/react-vis/src/legends/searchable-discrete-color-legend.js

@@ -40,7 +40,7 @@ const defaultProps = {
       item =>
         String(item.title || item)
           .toLowerCase()
-          .indexOf(s) !== -1
+          .indexOf(s.toLowerCase()) !== -1
     )
 };