constructor(program) {
    this.program = program;
  }
A simple tool to make behavior and API consistent between commands
the user wraps in this.

Usage:

```
let npm = new CommandGenerator('npm');
npm.invoke('install', 'ember-source', '--save-dev');
```

@private
@class CommandGenerator
@constructor
@param {Path} program The path to the command.
@return {Function} A command helper.