Removing select_subptotocol as it breaks in tornado 5+; Include nano

Dockerfile

@@ -1,5 +1,7 @@
 FROM debian:buster-slim
 
+COPY . /iris
+
 RUN set -ex \
 # Official Mopidy install for Debian/Ubuntu along with some extensions
 # (see https://docs.mopidy.com/en/latest/installation/debian/ )
@@ -15,6 +17,7 @@ RUN set -ex \
        python-pykka \
        python-tornado \
        git \
+       nano \
  && curl -L https://apt.mopidy.com/mopidy.gpg | apt-key add - \
  && curl -L https://apt.mopidy.com/mopidy.list -o /etc/apt/sources.list.d/mopidy.list \
  && apt-get update \