Refactor AnnotateRoutes.annotate_routes and .rewrite_contents_with_header (#729)

I refactored `AnnotateRoutes.annotate_routes` and `.rewrite_contents_with_header` in order to add an empty string to `new_content` array in `.annotate_routes`.

I will refactor `.rewrite_contents_with_header` more, and remove `. rewrite_contents_with_header` in the next PR.

Author: nard-tech

lib/annotate/annotate_routes.rb

@@ -65,9 +65,6 @@ def routes_file
     def rewrite_contents_with_header(existing_text, header, options = {})
       content, header_position = strip_annotations(existing_text)
       new_content = annotate_routes(header, content, header_position, options)
-
-      # Make sure we end on a trailing newline.
-      new_content << '' unless new_content.last == ''
       new_text = new_content.join("\n")
 
       if existing_text == new_text
@@ -195,6 +192,9 @@ def annotate_routes(header, content, header_position, options = {})
         new_content = magic_comments_map + content + header
       end
 
+      # Make sure we end on a trailing newline.
+      new_content << '' unless new_content.last == ''
+
       new_content
     end