Updated different platform example

Fauxhai does not have 5.4 information anymore leading to weird error when using it as-is. Replaced with 5.10 which should fix usage of those that copy/paste it directly.

Here the error I was facing when using original value:

```
 Failure/Error: ChefSpec::Runner.new(:platform => 'centos', :version => '5.4').converge(described_recipe)
     Fauxhai::Exception::InvalidPlatform:
       Could not find platform 'centos/5.4' in any of the sources!
     # ./spec/recipes/default_spec.rb:15:in `block (2 levels) in <top (required)>'
     # ./spec/recipes/default_spec.rb:19:in `block (2 levels) in <top (required)>'
```

Regards,
Matt