Simplify driver installation process

[aik099]

Changed error message formatting, that is shown, when driver package isn't installed.

Before PR:

Install MinkSelenium2Driver in order to use selenium2 driver.

After PR:

The "selenium2" driver package is not installed. Please follow installation instructions at https://packagist.org/packages/behat/mink-selenium2-driver.

[codecov]

Codecov Report

Attention: Patch coverage is 90.00000% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 82.98%. Comparing base (64070d5) to head (86ce20f).

Files	Patch %	Lines
...k099/PHPUnit/MinkDriver/Selenium2DriverFactory.php	33.33%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #133      +/-   ##
============================================
- Coverage     86.09%   82.98%   -3.12%     
- Complexity      326      328       +2     
============================================
  Files            28       29       +1     
  Lines           856      864       +8     
============================================
- Hits            737      717      -20     
- Misses          119      147      +28     

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