Steps to reproduce the issue

clone, build robo and
sudo vendor/bin/robo run:test
choose 5 then 1
[5] install/InstallWeblinksCest.php
[1] All

Expected result

Install Joomla and Weblinks

Actual result

Acceptance Tests (2) -------------------------------------------------------------------------------------------------------------------------------------
Modules: JoomlaBrowser, AcceptanceHelper

InstallWeblinksCest: Install joomla
Signature: InstallWeblinksCest:installJoomla
Test: tests/acceptance/install/InstallWeblinksCest.php:installJoomla
Scenario --
WebDriver::debugWebDriverLogs method has been called when webDriver is not set
WebDriver::_saveScreenshot method has been called when webDriver is not set
WebDriver::_savePageSource method has been called when webDriver is not set
Screenshot and page source were saved into '/var/www/html/weblinks/tests/_output/' dir
ERROR
.
.
.

1. InstallWeblinksCest: Install joomla
   Test tests/acceptance/install/InstallWeblinksCest.php:installJoomla

[Facebook\WebDriver\Exception\UnknownServerException] The driver executable does not exist: /var/www/html/weblinks/vendor/joomla-projects/selenium-server-standalone/bin/webdrivers/gecko/geckodriver_linux_64

System information (as much as possible)

Ubuntu 16.04.5 LTS
PHP 7.2.9-1+ubuntu16.04.1+deb.sury.org+1 (cli) (built: Aug 19 2018 07:16:12) ( NTS )
Server version: Apache/2.4.18 (Ubuntu)

Additional comments

driver appears to be there
$ ll /var/www/html/weblinks/vendor/joomla-projects/selenium-server-standalone/bin/webdrivers/gecko/geckodriver_linux_64
-rwxr-xr-x 1 gord gord 5593244 Feb 21 2017 /var/www/html/weblinks/vendor/joomla-projects/selenium-server-standalone/bin/webdrivers/gecko/geckodriver_linux_64*