Fix docker commands to work on ARM systems like macOS M1 (#1408)

scripts/in-docker.sh

@@ -11,6 +11,7 @@ fi
 # Taken from https://www.electron.build/multi-platform-build#docker
 # Pass through any vars prefixed with INDOCKER_, removing the prefix
 docker run --rm -ti \
+ --platform linux/amd64 \
  --env-file <(env | grep -E '^INDOCKER_' | sed -e 's/^INDOCKER_//') \
  --env ELECTRON_CACHE="/root/.cache/electron" \
  --env ELECTRON_BUILDER_CACHE="/root/.cache/electron-builder" \