Fix save method if there are no image manipulations

[moisish]

After the change on this commit bf0307c#diff-a4f3311910f99a1fe69b5fab2bcdb806288e552fe7ad5610ddb90f6a331aca37 the save method requires the spatie/image dependency even if you don't have any image manipulations.

Previously you could save an image without the need of the image dependency.

This test couldn't catch the issue because the dependency is not missing.

it('can take a high density screenshot', function () {
    $targetPath = __DIR__.'/temp/testScreenshot.png';

    Browsershot::url('https://example.com')
        ->deviceScaleFactor(2)
        ->save($targetPath);

    expect($targetPath)->toBeFile();
});

[moisish]

The tests are passing on my machine not sure why they are failing

[freekmurze]

Thanks!

[clementmas]

I was about to PR that fix after seeing some local Class "Imagick" not found errors. Thanks @moisish!