Update pl.xliff

[ioleo]

trafficstars

Added missing translations (compare to ru.xliff).

Please tag minor release when you merge this.

[ioleo]

Updated one last translation I've missed yesterday

[ioleo]

Updated the-checkbox-should-not-be-checked translation so it's not the same as the-checkbox-is-unchecked translation.

[ioleo]

Removed (?:|że ) which is unnecessary (equivalent of (?:|that )). The pl behat @Given already has Zakładając or Zakładając, że definition.

[ioleo]

Fixed missing semicolon. The regexp is now correct.

[ioleo]

Marked some words as optional.