Added a space before all entries in @mention autocomplete (#3605)

webapp/components/suggestion/at_mention_provider.jsx

@@ -80,6 +80,7 @@ class AtMentionSuggestion extends Suggestion {
                         {'@' + username}
                     </span>
                     <span className='mention__fullname'>
+                        {' '}
                         {description}
                     </span>
                 </div>