Uses Pipenv to pin version whilst making upgrades easy.

Dockerfile

@@ -10,14 +10,17 @@ RUN set -x \
         openssh \
         openssl \
         py-crypto \
-        py-pip \
         py-paramiko \
         py-setuptools \
         rsync \
- && update-ca-certificates \
- && pip install \
-      pydrive==1.3.1 \
-      fasteners==0.14.1 \
+ && update-ca-certificates
+
+COPY Pipfile Pipfile.lock /
+
+RUN set -x \
+ && apk add --no-cache py-pip \
+ && pip install pipenv \
+ && pipenv install --system --deploy \
  && apk del --purge py-pip \
  && adduser -D -u 1896 duplicity \
  && mkdir -p /home/duplicity/.cache/duplicity \