use sh syntax

Author: aptalca

Dockerfile.complex

@@ -9,12 +9,12 @@ RUN \
     curl && \
   echo "**** grab rclone ****" && \
   mkdir -p /root-layer && \
-  if [[ $(uname -m) == "x86_64" ]]; then \
+  if [ $(uname -m) = "x86_64" ]; then \
     echo "Downloading x86_64 tarball" && \
     curl -o \
       /root-layer/rclone.deb -L \
       "https://downloads.rclone.org/v1.47.0/rclone-v1.47.0-linux-amd64.deb"; \
-  elif [[ $(uname -m) == "aarch64" ]]; then \
+  elif [ $(uname -m) = "aarch64" ]; then \
     echo "Downloading aarch64 tarball" && \
     curl -o \
       /root-layer/rclone.deb -L \