message: Update rust version for linux.
diff: @@ -31,7 +31,7 @@ RUN pip3 install -U \
  setuptools \
  virtualenv
  -ENV RUST_ARCHIVE=rust-1.20.0-x86_64-unknown-linux-gnu.tar.gz
  +ENV RUST_ARCHIVE=rust-1.21.0-x86_64-unknown-linux-gnu.tar.gz
  ENV RUST_DOWNLOAD_URL=https://static.rust-lang.org/dist/$RUST_ARCHIVE
  RUN mkdir -p /rust
  