Fix variable expansion

Dockerfile

@@ -0,0 +1,23 @@
+# syntax = docker/dockerfile:1.2
+FROM rust:1.65.0 as base
+RUN cargo install cargo-chef
+RUN rustup component add rustfmt
+RUN apt-get update && apt-get install -y clang cmake ssh
+WORKDIR /app
+
+FROM base AS plan
+COPY . .
+WORKDIR /app
+RUN cargo chef prepare --recipe-path recipe.json
+
+FROM base as build
+COPY --from=plan /app/recipe.json recipe.json
+RUN cargo chef cook --release --recipe-path recipe.json
+COPY . .
+RUN cargo build --release --bin lite-rpc
+
+FROM debian:bullseye-slim as run
+RUN apt-get update && apt-get -y install ca-certificates libc6
+COPY --from=build /app/target/release/lite-rpc /usr/local/bin/
+
+CMD lite-rpc --rpc-url "$RPC_URL" --websocket-url "$WS_URL"