Fix issue updated_unix bug (#2204)

models/issue_comment.go

@@ -399,7 +399,11 @@ func createComment(e *xorm.Session, opts *CreateCommentOptions) (_ *Comment, err
 		if err != nil {
 			return nil, err
 		}
+	}
 
+	// update the issue's updated_unix column
+	if err = updateIssueCols(e, opts.Issue); err != nil {
+		return nil, err
 	}
 
 	// Notify watchers for whatever action comes in, ignore if no action type.