fix alt on emoji dropdown

app/javascript/mastodon/features/compose/components/emoji_picker_dropdown.js

@@ -389,7 +389,7 @@ class EmojiPickerDropdown extends React.PureComponent {
         <div ref={this.setTargetRef} className='emoji-button' title={title} aria-label={title} aria-expanded={active} role='button' onClick={this.onToggle} onKeyDown={this.onToggle} tabIndex={0}>
           {button || <img
             className={classNames('emojione', { 'pulse-loading': active && loading })}
-            alt='🙂'
+            alt='☕'
             src={`${assetHost}/emoji/2615.svg`}
           />}
         </div>