Merge command doesn't output working HTML

First off, thanks for writing this gem.  I ended up using it on a project, and while it helped me out immensely, I found that it didn't quite work out of the box.  One of the problems I faces was that the index.html file being generated was broken.  It looks like the Ruby code is writing the whole contents of an array out to the index.html file, including the '[' and ']' characters.  This pull request outputs pure html, and also updates the Rakefile so that the merge task works without error.

I hope you might find it useful.