Switch to ubuntu

... and use standard miller package

Dockerfile

@@ -1,4 +1,4 @@
-FROM alpine
+FROM ubuntu
 LABEL org.opencontainers.image.title="gtfs-hub"
 LABEL org.opencontainers.image.description="Collecting, shape-enhancing, validating, fixing and (partially) merging GTFS feeds."
 LABEL org.opencontainers.image.authors="MITFAHR|DE|ZENTRALE <[email protected]>"
@@ -8,16 +8,23 @@ LABEL org.opencontainers.image.licenses="GPL-3.0-only"
 
 WORKDIR /gtfs-hub
 
-RUN apk add --update --no-cache \
-  make \
-  bash \
-  moreutils \
-  curl \
-  zip \
-  docker-cli
-# miller is included in the "community" branch, not in the "main" branch.
-# https://github.com/johnkerl/miller/issues/293#issuecomment-687661421
-RUN apk add --no-cache -X http://dl-cdn.alpinelinux.org/alpine/edge/community miller
+RUN apt-get update && apt-get install -y \
+    make \
+    bash \
+    moreutils \
+    curl \
+    zip \
+    miller \
+    ca-certificates \
+    gnupg \
+    lsb-release \
+  && curl -fsSL https://download.docker.com/linux/ubuntu/gpg | gpg --dearmor -o /usr/share/keyrings/docker-archive-keyring.gpg \
+  && echo \
+    "deb [arch=$(dpkg --print-architecture) signed-by=/usr/share/keyrings/docker-archive-keyring.gpg] https://download.docker.com/linux/ubuntu \
+    $(lsb_release -cs) stable" | tee /etc/apt/sources.list.d/docker.list > /dev/null \
+  && apt-get update && apt-get install -y \
+    docker-ce-cli \
+  && apt-get clean
 
 ADD patch_raw_gtfs.sh patch_filtered_gtfs.sh ./
 ADD download.sh .