Removing dependency for tornado, use whatever Mopidy provides, fixes #443

Dockerfile

@@ -1,4 +1,4 @@
-FROM debian:stretch-slim
+FROM debian:buster-slim
 
 RUN set -ex \
 # Official Mopidy install for Debian/Ubuntu along with some extensions
@@ -13,6 +13,7 @@ RUN set -ex \
        gstreamer1.0-plugins-bad \
        python-crypto \
        python-pykka \
+       python-tornado \
        git \
  && 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 \

setup.py

@@ -24,8 +24,7 @@ setup(
         'Mopidy >= 2.0',
         'Mopidy-Local-Images >= 1.0',
         'ConfigObj >= 5.0.6',
-        'requests >= 2.0.0',
-        'tornado >= 3.2, < 5.0'
+        'requests >= 2.0.0'
     ],
     classifiers=[
         'Environment :: No Input/Output (Daemon)',