trim placeholder to remove whitespaces

Just another try to explain why my changes are required ;-)

in the template we can write {% trans %}placeholder{% endtrans %} or {% trans %} placeholder {% endtrans %}
it would both match witch the string 'placeholder' in the translation file

when we call the console script translation:update the first would be created to 'placeholder' and the second to ' placeholder ', which are two different values, but the first one is correct and work with both trans tags.