Prevent wasted render in load_more.js (#3402)

app/javascript/mastodon/components/load_more.js

@@ -2,14 +2,20 @@ import React from 'react';
 import { FormattedMessage } from 'react-intl';
 import PropTypes from 'prop-types';
 
-const LoadMore = ({ onClick }) => (
-  <button className='load-more' onClick={onClick}>
+class LoadMore extends React.PureComponent {
+
+  static propTypes = {
+    onClick: PropTypes.func,
+  }
+
+  render() {
+    return (
+      <button className='load-more' onClick={this.props.onClick}>
         <FormattedMessage id='status.load_more' defaultMessage='Load more' />
       </button>
-);
+    );
+  }
 
-LoadMore.propTypes = {
-  onClick: PropTypes.func,
-};
+}
 
 export default LoadMore;