Merge pull request #240 from JohnTitor/gha

Tweak GHA config

.github/workflows/main.yml

@@ -6,7 +6,7 @@ jobs:
     name: Test
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@master
+    - uses: actions/checkout@v2
     - name: Update rustup
       run: rustup self update
     - name: Install Rust
@@ -15,10 +15,12 @@ jobs:
         rustup toolchain install nightly -c rust-docs
         rustup default nightly
     - name: Install mdbook
+      env:
+        MDBOOK_VER: v0.4.3
       run: |
         mkdir bin
-        curl -sSL https://github.com/rust-lang/mdBook/releases/download/v0.3.5/mdbook-v0.3.5-x86_64-unknown-linux-gnu.tar.gz | tar -xz --directory=bin
-        echo "##[add-path]$(pwd)/bin"
+        curl -sSL https://github.com/rust-lang/mdBook/releases/download/${{ env.MDBOOK_VER }}/mdbook-${{ env.MDBOOK_VER }}-x86_64-unknown-linux-gnu.tar.gz | tar -xz --directory=bin
+        echo "$(pwd)/bin" >> $GITHUB_PATH
     - name: Report versions
       run: |
         rustup --version