Bugfix: cannot set 'mode' with DI configuration.

[antoniocambados]

With this bugfix you can set the mode with any of these configurations:

phpmob_ace:
    configs:
        html:
            autoScrollEditorIntoView: true
            maxLines: 20
            minLines: 5
            mode: 'ace/mode/html'
            theme: 'ace/theme/github'

public function buildForm(FormBuilderInterface $builder, array $options)
{
    $builder
        ->add('html', AceType::class, [
            'required'    => false,
            'mode' => 'html',
        ]);
}

public function buildForm(FormBuilderInterface $builder, array $options)
{
    $builder
        ->add('html', AceType::class, [
            'required'    => false,
            'config' => [
                'mode' => 'html'
            ]
        ]);
}

When combining these methods, the first one has less priority than the last one.

Fixes #1