Fixed string utility examples

[mjomble]

Some of the documentation examples are incorrect and make it seem like there's additional hidden functionality for removing whitespace.

I tested them in artisan tinker:

> Str::of('Arkansas is quite beautiful!')->remove('quite')
= Illuminate\Support\Stringable {#7012
    value: "Arkansas is  beautiful!",
  }

> Str::of('Foo Bar')->ucsplit()
= Illuminate\Support\Collection {#7005
    all: [
      "Foo ",
      "Bar",
    ],
  }