Explicitly use / as home directory, not /root

The home directory seems to have changed, and the value of $HOME is /config, which is odd.

Dockerfile

@@ -19,12 +19,14 @@ COPY ./fonts ./fonts
 # NOT FOR PRODUCTION
 COPY ./.env ./.env
 
+ENV HOME=/
+
 # Copy a LibreOffice config file which uses Times New Roman as the
 # default font -- see README.txt
-RUN mkdir -p /root/.config/libreoffice/4/user
-RUN mkdir /root/.config/fontconfig
-RUN cp registrymodifications.xcu /root/.config/libreoffice/4/user/registrymodifications.xcu
-RUN cp fonts.conf /root/.config/fontconfig/fonts.conf
+RUN mkdir -p $HOME/.config/libreoffice/4/user
+RUN mkdir $HOME/.config/fontconfig
+RUN cp registrymodifications.xcu $HOME/.config/libreoffice/4/user/registrymodifications.xcu
+RUN cp fonts.conf $HOME/.config/fontconfig/fonts.conf
 
 # Install fonts
 RUN mkdir -p /usr/share/fonts/truetype/docker-context