message: chore: override nightly toolchain in coverage workflow
  Fix the error that grcov could not find llvm-profdata:
diff: @@ -13,10 +13,11 @@ jobs:
  if: |
  github.repository_owner == 'nervosnetwork'
  steps:
  - - name: install nightly
  - run: |
  - rustup toolchain list | { grep 'nightly' || rustup install nightly; }
  - uses: actions/checkout@v2
  + - uses: actions-rs/toolchain@v1
  + with:
  + toolchain: nightly
  + override: true
  - name: unit coverage
  run: make cov
  - name: integration cov
  