Laravel 5.4 on PHP 7.0: PDO Exception - Could not find driver (MySQL)
Same problem, ubuntu 17.10, Laravel 5.5.
$ sudo apt install php7.1-pdo php7.1-mysql
A nice quick fix, hope this helps
As an alternative solution be sure you have installed php7-mysql
try to run command below
sudo apt install php7.0-mysql
or, if you want to automatically install the current version
sudo apt install php-mysql