adjust supercronic download to allow multiarch builds

Dockerfile

@@ -22,12 +22,16 @@ RUN DEBIAN_FRONTEND=noninteractive dpkg-reconfigure locales \
 
 ENV LC_ALL C.UTF-8
 
-ENV SUPERCRONIC_URL=https://github.com/aptible/supercronic/releases/download/v0.1.3/supercronic-linux-amd64 \
-    SUPERCRONIC=supercronic-linux-amd64 \
-    SUPERCRONIC_SHA1SUM=96960ba3207756bb01e6892c978264e5362e117e
+ARG ARCH=amd64
+ENV SUPERCRONIC_URL=https://github.com/aptible/supercronic/releases/download/v0.1.3/supercronic-linux-$ARCH \
+    SUPERCRONIC=supercronic-linux-$ARCH \
+    SUPERCRONIC_amd64_SHA1SUM=96960ba3207756bb01e6892c978264e5362e117e \
+    SUPERCRONIC_arm_SHA1SUM=8c1e7af256ee35a9fcaf19c6a22aa59a8ccc03ef \
+    SUPERCRONIC_arm64_SHA1SUM=f0e8049f3aa8e24ec43e76955a81b76e90c02270 \
+    SUPERCRONIC_SHA1SUM="SUPERCRONIC_${ARCH}_SHA1SUM"
 
 RUN curl -fsSLO "$SUPERCRONIC_URL" \
- && echo "${SUPERCRONIC_SHA1SUM}  ${SUPERCRONIC}" | sha1sum -c - \
+ && echo "${!SUPERCRONIC_SHA1SUM}  ${SUPERCRONIC}" | sha1sum -c - \
  && chmod +x "$SUPERCRONIC" \
  && mv "$SUPERCRONIC" "/usr/local/bin/${SUPERCRONIC}" \
  && ln -s "/usr/local/bin/${SUPERCRONIC}" /usr/local/bin/supercronic