Add via to the toString method

Author: PierreBtz

src/main/java/org/zendesk/client/v2/model/Comment.java

@@ -131,6 +131,7 @@ public String toString() {
                 ", attachments=" + attachments +
                 ", createdAt=" + createdAt +
                 ", uploads=" + uploads +
+                ", via=" + via +
                 '}';
     }
-}
+}