Add prefer stable flag to composer.json.
Add prefer stable flag to composer.json.

kristijanhusak/laravel-form-builder,Devitek/laravel-form-builder,mstaack/laravel-form-builder,leohmoraes/laravel-form-builder,theshaunwalker/laravel-form-builder,tantam/laravel-form-builder,barryvdh/laravel-form-builder