change lts to v12

Dockerfile

@@ -1,10 +1,10 @@
-FROM node:lts
+FROM node:12
 WORKDIR /data
 COPY ./ffmpeg.tgz /
 RUN apt-get update && \
-  apt-get full-upgrade -y && \
   apt-get install -y unoconv curl imagemagick graphicsmagick curl wget python3 python3-pip qpdf poppler-utils git curl wget && \
   apt-get clean && \
   mkdir -p /usr/local/bin && \
   tar zxvf /ffmpeg.tgz -C /usr/local/bin && \
-  rm /ffmpeg.tgz
+  rm /ffmpeg.tgz && \
+  rm -rf /var/lib/apt/lists