fix Docker image build

Author: anweiss

Dockerfile

@@ -1,7 +1,13 @@
-FROM ekidd/rust-musl-builder:1.57.0 AS builder
+FROM rust:slim AS builder
+RUN apt update && apt install -y musl-tools musl-dev
+RUN apt-get install -y build-essential
+RUN yes | apt install gcc-x86-64-linux-gnu
+ENV TARGET x86_64-unknown-linux-musl
+RUN rustup target add "$TARGET"
+ENV RUSTFLAGS='-C linker=x86_64-linux-gnu-gcc'
 COPY . ./
-RUN cargo b --release --bin cddl
+RUN cargo b --release --bin cddl --target "$TARGET"
 
 FROM scratch
-COPY --from=builder /home/rust/src/target/x86_64-unknown-linux-musl/release/cddl /cddl
+COPY --from=builder /target/x86_64-unknown-linux-musl/release/cddl /cddl
 ENTRYPOINT [ "/cddl" ]