Update Dockerfile

Dockerfile

 FROM buildpack-deps:buster-curl
 
-RUN apt-get update && apt-get install -y ca-certificates libgs9 && \
+RUN apt-get update && apt-get install -y ca-certificates libgs9 wkhtmltopdf && \
 apt-get clean autoclean && \
 apt-get autoremove --yes && \
 rm -rf /var/lib/{apt,dpkg,cache,log}