⬆️ rust 1.64 for ptth_quic's relay app

prototypes/quic_demo/Dockerfile

@@ -1,8 +1,8 @@
 # https://whitfin.io/speeding-up-rust-docker-builds/
 # TODO: https://stackoverflow.com/questions/57389547/how-to-define-the-context-for-a-docker-build-as-a-specific-commit-on-one-of-the
 
-# rust:1.50-slim-buster
-FROM rust@sha256:5dd85eb0c60bbdea14a6ecba1f6fe4a0f5c878bcf06d2cdfae0aff3a19ed4b10 as build
+# rust:1.64-slim-buster
+FROM rust@sha256:7da4fbd2dc7176746e8e5c371aeb0bbe742598c4906fa48cb2d87a4b89d50357 as build
 
 WORKDIR /
 ENV USER root