Fix ARG usage

https://docs.docker.com/engine/reference/builder/#understand-how-arg-and-from-interact

Dockerfile

@@ -2,6 +2,7 @@ ARG NGINX_TMP_INSTALL_DIR=/tmp/nginx-rtmp
 
 FROM alpine:latest as builder
 
+ARG NGINX_TMP_INSTALL_DIR
 ENV NGINX_VERSION=1.18.0
 ENV NGINX_RTMP_MODULE_COMMIT=23ec4ce2d769830124abf3be1353dd9b105ab09c
 
@@ -41,6 +42,10 @@ COPY nginx.conf ${NGINX_TMP_INSTALL_DIR}/usr/local/nginx/conf/nginx.conf
 
 FROM alpine:latest
 
+ARG NGINX_TMP_INSTALL_DIR
+
+RUN apk --no-cache add libssl1.1 pcre zlib
+
 # Copy installed nginx from previous stage
 COPY --from=builder ${NGINX_TMP_INSTALL_DIR} /