Inserting newline requires double-quoted string

lib/annotate/annotate_models.rb

@@ -146,7 +146,7 @@ module AnnotateModels
           if new_content == old_content
             old_content.sub!(encoding, '')
             new_content = options[:position] == 'after' ?
-              (encoding_header + (old_content =~ /\n$/ ? old_content : old_content + '\n') + info_block) :
+              (encoding_header + (old_content =~ /\n$/ ? old_content : old_content + "\n") + info_block) :
               (encoding_header + info_block + old_content)
           end