Laravel v5.8.3 is released in 2019/03/05, here are the changes we`ve merged into this release.

Added

• Added Collection::countBy() (#27770)
• Added protected EloquentUserProvider::newModelQuery() (#27734, 9bb7685)
• Added protected StartSession::saveSession() method (#27771, 76c7126)
• Allow belongsToMany to take Model/Pivot class name as a second parameter (#27774)

Fixed

• Fixed environment variable parsing (#27706)
• Fixed guessed policy names when using Gate::forUser (#27708)
• Fixed via as string in the Notification (#27710)
• Fixed StartSession middleware (499e4fe)
• Fixed stack channel's bug related to the level (#27726, bc884bb)
• Fixed email validation for not string values (#27735)

Changed

• Check if MessageBag is empty before checking keys exist in the MessageBag (#27719)

GitHub:https://github.com/laravel/framework/releases/tag/v5.8.3