master: add gosu to runtime stage

Author: willcl-ark

master/Dockerfile

@@ -59,7 +59,7 @@ ENV BITCOIN_DATA=/home/bitcoin/.bitcoin
 RUN groupadd --gid ${GID} bitcoin \
   && useradd --create-home --no-log-init -u ${UID} -g ${GID} bitcoin \
   && apt-get update -y \
-  && apt-get install -y libevent-dev libboost-dev libsqlite3-dev libzmq3-dev systemtap-sdt-dev --no-install-recommends \
+  && apt-get install -y gosu libevent-dev libboost-dev libsqlite3-dev libzmq3-dev systemtap-sdt-dev --no-install-recommends \
   && apt-get clean \
   && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*