Make Pandov version configurable

Dockerfile

 FROM alpine:edge
 
-# RUN apt-get update -y && apt-get install -y pandoc pandoc-data
+ENV PANDOC_VERSION=2.7.3
 
-RUN apk add ttf-linux-libertine
-RUN apk add texlive-full
-RUN apk add hugo git ttf-linux-libertine
+RUN apk add --no-cache ttf-linux-libertine
+RUN apk add --no-cache texlive-full
+RUN apk add --no-cache hugo git ttf-linux-libertine
 
-RUN apk add ca-certificates wget \
-  && wget -O /tmp/pandoc.tar.gz https://github.com/jgm/pandoc/releases/download/2.7.3/pandoc-2.7.3-linux.tar.gz \
+RUN apk add --no-cache ca-certificates wget \
+  && wget -O /tmp/pandoc.tar.gz https://github.com/jgm/pandoc/releases/download/${PANDOC_VERSION}/pandoc-${PANDOC_VERSION}-linux.tar.gz \
   && tar xvzf /tmp/pandoc.tar.gz --strip-components 1 -C /usr/local/ \
   && update-ca-certificates \
   && apk del wget \
   && rm /tmp/pandoc.tar.gz
 
-
-# RUN wget -q https://github.com/gohugoio/hugo/releases/download/v0.55.6/hugo_0.55.6_Linux-64bit.deb -O /tmp/hugo.deb && dpkg -i /tmp/hugo.deb
-