fix pll lang url failing test

[diggy]

cf. #61

    When I run `wp pll lang url nl`                               # features/steps/when.php:29
    Then STDOUT should contain:                                   # features/steps/then.php:15
      """
      http://example.com/?lang=nl
      """
      $ wp pll lang url nl
      http://example.com/
      
      exit status: 0

[diggy]

see polylang/polylang@bd235ed