poc/Dockerfile: tidy it a little bit

poc/Dockerfile

@@ -1,7 +1,20 @@
 FROM python:3.7-alpine
-RUN apk update && apk add bash curl coreutils file
+
-RUN pip install pipenv
 COPY Pipfile Pipfile.lock /tmp/
-RUN cd /tmp && pipenv install --system --deploy
+
 COPY bin/* /usr/bin/
+
+WORKDIR /tmp
+
+RUN apk upgrade --update-cache;                 \
+    apk add                                     \
+        bash                                    \
+        curl                                    \
+        coreutils                               \
+        file;                                   \
+                                                \
+    pip install pipenv;                         \
+                                                \
+    pipenv install --system --deploy;
+
 ENTRYPOINT ["/usr/bin/kapow"]