Update Dockerfile

Author: emalinowski

Dockerfile

@@ -21,7 +21,7 @@ COPY --from=builder /etc_passwd /etc/passwd
 COPY --from=builder /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/
 COPY --from=builder /go/src/github.com/abutaha/aws-es-proxy/aws-es-proxy /aws-es-proxy
 
-ENV PORT_NUM 9200
+ENV PORT_NUM=9200
 EXPOSE ${PORT_NUM}
 
 USER nobody