update Dockerfile to use LibreOffice v6.1.6

 * v6.1.5 is no longer available from their archive.

Author: felliott

Dockerfile

@@ -55,8 +55,8 @@ RUN usermod -d /home www-data \
     && pip install setuptools==37.0.0 \
     && mkdir -p /code
 
-ENV LIBREOFFICE_VERSION 6.1.5
-ENV LIBREOFFICE_ARCHIVE LibreOffice_6.1.5_Linux_x86-64_deb.tar.gz
+ENV LIBREOFFICE_VERSION 6.1.6
+ENV LIBREOFFICE_ARCHIVE LibreOffice_6.1.6_Linux_x86-64_deb.tar.gz
 ENV LIBREOFFICE_MIRROR_URL https://download.documentfoundation.org/libreoffice/stable/
 RUN apt-get update \
     && apt-get install -y \