Prefer "geckodriver" name when looking up binary

Previously, binaries were shipped with version suffix, but not anymore.
Closes #5240.

Author: p0deje

rb/lib/selenium/webdriver/firefox/service.rb

@@ -24,7 +24,7 @@ module Firefox
 
       class Service < WebDriver::Service
         DEFAULT_PORT = 4444
-        @executable = 'geckodriver*'.freeze
+        @executable = 'geckodriver'.freeze
         @missing_text = <<-ERROR.gsub(/\n +| {2,}/, ' ').freeze
           Unable to find Mozilla geckodriver. Please download the server from
           https://github.com/mozilla/geckodriver/releases and place it somewhere on your PATH.