Add missing rsync.

Dockerfile

@@ -47,7 +47,7 @@ FROM python:3.6-stretch
 
 RUN apt-get update \
     && apt-get install -y --no-install-recommends \
-    libmhash2 \
+    rsync libmhash2 \
     && rm -rf /var/lib/apt/lists/*
 
 #RUN apk add coreutils