Apache: vhost: fix template file source.

The template file was listed as an actual file whilst it is actually a
template file. This should be reflected as such.

As you can see [here](https://github.com/openminds/sneakers/tree/master/chef/cookbooks/apache/files/default) there is no rack_vhost.conf file, this file 
is [here](https://github.com/openminds/sneakers/blob/master/chef/cookbooks/apache/templates/default/rack_vhost.conf.erb) (although with a slightly different name).

I noticed this when I used the following settings:

```blog:
  app_directory: "/Users/jelmersnoeck/Projects/blog"
  type: "ruby193"
  http_port: 8040
  memory: 1024
```

I got the following error:

```
[2013-06-03T21:07:44+02:00] FATAL: Chef::Exceptions::FileNotFound: cookbook_file[/etc/apache2/sites-available/default] (apache::passenger line 55) had an error: Chef::Exceptions::FileNotFound: Cookbook 'apache' (0.1.0) does not contain a file at any of these locations:
  files/debian-6.0.7/rack_vhost.conf.erb
  files/debian/rack_vhost.conf.erb
  files/default/rack_vhost.conf.erb
```