message: simplify Dockerfile
diff: @@ -11,7 +11,7 @@ ENV RUSTUP_HOME=/usr/local/rustup \
  RUN set -eux; \
  dpkgArch="$(dpkg --print-architecture)"; \
  - case "$dpkgArch##*-" in \
  + case $dpkgArch in \
  amd64) rustArch='x86_64-unknown-linux-gnu'; rustupSha256='3dc5ef50861ee18657f9db2eeb7392f9c2a6c95c90ab41e45ab4ca71476b4338' ;; \
  armhf) rustArch='armv7-unknown-linux-gnueabihf'; rustupSha256='67777ac3bc17277102f2ed73fd5f14c51f4ca5963adadf7f174adf4ebc38747b' ;; \
  arm64) rustArch='aarch64-unknown-linux-gnu'; rustupSha256='32a1532f7cef072a667bac53f1a5542c99666c4071af0c9549795bbdb2069ec1' ;; \
  