Replace last_author with last-author

app/assets/stylesheets/conversations.scss

@@ -65,7 +65,7 @@
 
     &:hover:not(.selected), &.selected {
       .subject,
-      .last_author,
+      .last-author,
       .last_message {
         color: $white;
       }
@@ -86,14 +86,14 @@
     &.unread { background-color: $background-grey; }
     &.selected { background-color: $brand-primary; }
 
-    .last_author, .last_message {
+    .last-author, .last_message {
       font-size: 12px;
       line-height: 15px;
       overflow: hidden;
       text-overflow: ellipsis;
       white-space: nowrap;
     }
-    .last_author { color: $text-dark-grey; }
+    .last-author { color: $text-dark-grey; }
 
     .message-count, .unread-message-count {
       margin-left: 3px;

app/assets/stylesheets/mobile/mobile.scss

@@ -486,7 +486,7 @@ select {
   margin-bottom: 5px;
 }
 
-.last_author {
+.last-author {
   position: relative;
   margin: 10px 10px 2px;
   float: right;

app/views/conversations/_conversation.haml

@@ -26,7 +26,7 @@
             = conversation.subject
         .timestamp
           = timeago(conversation.updated_at)
-        .last_author
+        .last-author
           - if conversation.last_author.present?
             = conversation.last_author.name
         .last_message

app/views/conversations/_conversation.mobile.haml

@@ -9,7 +9,7 @@
         = render partial: "conversation_subject",
                  locals:  { conversation: conversation, unread_count: visibility.unread }
 
-        .last_author
+        .last-author
           .timestamp
             = timeago(conversation.updated_at)