ensure every <li> has a key

src/components/category.js

@@ -198,7 +198,7 @@ export default class Category extends React.Component {
         <ul className="emoji-mart-category-list">
         {emojis &&
           emojis.map((emoji) => (
-              <li>
+              <li key={emoji.id || emoji}>
                 {NimbleEmoji({ emoji: emoji, data: this.data, ...emojiProps })}
               </li>
             )

src/components/emoji/nimble-emoji.js

@@ -185,7 +185,6 @@ const NimbleEmoji = (props) => {
   } else {
     return (
       <button
-        key={props.emoji.id || props.emoji}
         onClick={(e) => _handleClick(e, props)}
         onMouseEnter={(e) => _handleOver(e, props)}
         onMouseLeave={(e) => _handleLeave(e, props)}