Add chaining of arguments

To prevent cases as:

```ruby
bundle = stubbed_env.stub_command('bundle')
expect(bundle.with_args('exec', 'rake', 'test')).to be_called
expect(bundle.with_args('exec', 'rake', 'release')).to be_called
```

I would like to do:

```ruby
rake = stubbed_env.stub_command('bundle').with_args('exec', 'rake')
expect(rake.with_args('test')).to be_called
expect(rake.with_args('release')).to be_called
```