xslt-config: not found

Hi

I've tried to build from your Dockerfile but I had errors with libxml and libxslt : xslt-config: not found.

Had to add 
RUN apt-get -yqq install git libffi-dev libssl-dev libxml2-dev libxslt1-dev
instead of
RUN apt-get -yqq install git libffi-dev libssl-dev

Hope it can help.

Regards