Merge branch 'feature--slim-down-the-docker-image' into staging

Dockerfile

@@ -26,13 +26,20 @@ COPY assets/seafile.list /etc/apt/sources.list.d/
 COPY utils/build/import-seafile-apt-key.sh /
 RUN /bin/bash /import-seafile-apt-key.sh ;\
     apt-get update ;\
-    apt-get install -o Dpkg::Options::="--force-confold" -y seafile-cli supervisor ;\
-    apt-get autoclean ;\
-    rm -f \
-        /var/log/fsck/*.log \
-        /var/log/apt/*.log \
-        /var/cache/debconf/*.dat-old \
-        /import-seafile-apt-key.sh 
+    apt-get install \
+        -o Dpkg::Options::="--force-confold" \
+        -y \
+            seafile-cli \
+            supervisor ;\
+    apt-get clean ;\
+    apt-get autoclean \
+        -o APT::Clean-Installed=true ;\
+    rm \
+        -f \
+            /var/log/fsck/*.log \
+            /var/log/apt/*.log \
+            /var/cache/debconf/*.dat-old \
+            /import-seafile-apt-key.sh 
 
 # Create the seafile client user.
 ENV UNAME=seafuser