message: ci: update toolchain for building api doc
diff: @@ -21,6 +21,8 @@ jobs:
  mkdir mdbook
  curl -Lf https://github.com/rust-lang/mdBook/releases/download/v0.4.9/mdbook-v0.4.9-x86_64-unknown-linux-gnu.tar.gz | tar -xz --directory=./mdbook
  echo `pwd`/mdbook >> $GITHUB_PATH
  + - name: Update toolchain
  + run: rustup update --no-self-update stable && rustup default stable
  - name: Build API doc
  run: |
  cargo doc --document-private-items --no-deps
  