chore: Update Dockerfile to include custom sources.list for ffmpeg installation

Author: s045pd

Dockerfile

@@ -1,14 +1,7 @@
 FROM node:12.16.2-stretch
 
 
-ENV DEBIAN_FRONTEND=noninteractive
-RUN echo "deb http://deb.debian.org/debian stretch main" > /etc/apt/sources.list \
-	&& echo "deb-src http://deb.debian.org/debian stretch main" >> /etc/apt/sources.list \
-	&& echo "deb http://deb.debian.org/debian stretch-updates main" >> /etc/apt/sources.list \
-	&& echo "deb-src http://deb.debian.org/debian stretch-updates main" >> /etc/apt/sources.list \
-	&& echo "deb http://security.debian.org/debian-security stretch/updates main" >> /etc/apt/sources.list \
-	&& echo "deb-src http://security.debian.org/debian-security stretch/updates main" >> /etc/apt/sources.list
-
+COPY sources.list /etc/apt/sources.list
 RUN apt update && apt install ffmpeg -y