Moved prophecy-phpunit to require not require-dev

Things in `require-dev` are not included when other packages do `composer install --dev`.

Infact, I think everything in this bundle should be `require` and not `require-dev` as this package itself is only included in other bundles as `required-dev`.

__Informations:__

| Q             | A
| ------------- | ---
| Tests pass?   | n/a
| Fixed tickets | n/a
| BC Breaks     | no