Change certbot into letsencrypt

Dockerfile

@@ -2,7 +2,7 @@ FROM node:latest
 
 ENV HOSTNAME=${HOSTNAME:-haraka}
 
-RUN apt-get update && apt-get upgrade -y && apt-get install -y supervisor certbot && \
+RUN apt-get update && apt-get upgrade -y && apt-get install -y supervisor letsencrypt && \
     rm -rf /var/lib/apt/lists/* && \
     mkdir /var/log/supervisord && \
     groupadd -r haraka && \