Make storybook directive parsing more consistent with regular blade statements

[koenvu]

First of all, thank you for this package and the accompanying article 🙌 . We are looking into potentially using this in our projects.

One thing I noticed is that I could not use @storybook (['....']) (notice the whitespace). This PR makes it more consistent with how Laravel parses such statements. I had to check, but yes, in fact Laravel does allow the statement below, not just zero or one spaces 😅; this change is straight from their parser.

@foreach         (...)
    ...
@endforeach

[mrtimbrook]

I like it! Thanks!