Fix "cancel follow request" button having unreadable text in web UI (#11521)

Fix #11478

app/javascript/mastodon/components/button.js

@@ -12,6 +12,7 @@ export default class Button extends React.PureComponent {
     secondary: PropTypes.bool,
     size: PropTypes.number,
     className: PropTypes.string,
+    title: PropTypes.string,
     style: PropTypes.object,
     children: PropTypes.node,
   };
@@ -54,6 +55,7 @@ export default class Button extends React.PureComponent {
         onClick={this.handleClick}
         ref={this.setRef}
         style={style}
+        title={this.props.title}
       >
         {this.props.text || this.props.children}
       </button>