Merge pull request #1046 from palfrey/fix-mdbook

Fix mdbook build

.github/workflows/book.yml

@@ -2,8 +2,7 @@ name: Build and deploy documentation book
 
 on:
   push:
-    branches:
-      - master
+  pull_request:    
 
 jobs:
   book:
@@ -16,10 +15,23 @@ jobs:
           toolchain: stable
           override: true
 
+      - name: Cache dependencies
+        uses: actions/cache@v2
+        env:
+          cache-name: cache-mdbook
+        with:
+          path: |
+            ~/.cargo/.crates.toml
+            ~/.cargo/.crates2.json
+            ~/.cargo/bin
+            ~/.cargo/registry/index
+            ~/.cargo/registry/cache
+          key: ${{ runner.os }}-build-${{ env.cache-name }}-0.3 }}
+
       - name: Install mdbook
         run: |
           (test -x $HOME/.cargo/bin/cargo-install-update || cargo install cargo-update)
-          (test -x $HOME/.cargo/bin/mdbook || cargo install --vers "^0.2" mdbook)
+          (test -x $HOME/.cargo/bin/mdbook || cargo install --vers "^0.3" mdbook)
           cargo install-update -a
 
       - name: Build book
@@ -31,6 +43,7 @@ jobs:
 
       - name: Deploy book
         uses: JamesIves/github-pages-deploy-action@4.1.4
+        if: ${{ github.ref == 'refs/heads/master' }}
         with:
           branch: gh-pages
           folder: docs