Fix broken file references, making the gem mode unusable.

Fixes:

```
octopress at /Users/jfrisby/.rvm/gems/ruby-2.0.0-p0@mrjoy.com/bundler/gems/octopress-c1f6834c824f did not have a valid gemspec.
This prevents bundler from installing bins or native extensions, but that may not affect its functionality.
The validation message from Rubygems was:
  ["lib/octopress/scaffold/config/compass.rb", "lib/octopress/scaffold/config/rack.rb", "lib/octopress/scaffold/config/site.yml", "lib/octopress/scaffold/stylesheets/plugins/plugins.scss", "lib/octopress/scaffold/stylesheets/screen.scss"] are not files
```