fixed username button title

public/language/en/topic.json

@@ -1,5 +1,6 @@
 {
 	"profile": "Profile",
+	"posted_by": "Posted by",
 	"chat": "Chat",
 	"notify_me": "Be notified of new replies in this topic",
 	"favourite": "Favourite",

public/templates/topic.tpl

@@ -27,7 +27,7 @@
 
 						<div class="topic-buttons">
 							<div class="btn-group">
-								<button class="btn btn-sm btn-default dropdown-toggle" data-toggle="dropdown" type="button" title="[[topic:posted_by, {main_posts.username}]]">
+								<button class="btn btn-sm btn-default dropdown-toggle" data-toggle="dropdown" type="button" title="[[topic:posted_by]] {main_posts.username}">
 									<span class="username-field" href="/user/{main_posts.userslug}">{main_posts.username}&nbsp;</span>
 									<span class="caret"></span>
 								</button>