Fix command_to_module_name not converting snakecased names properly

Currently, snake cased project names did not get converted properly into modules from `Mix.Utils.command_to_module_name`, i.e.:

```elixir
Mix.Utils.command_to_module_name "my_app.task"
=> "My_app.Task"
```

This PR uses `camelize` to properly convert the commands to module namespaces.