CI: Fetch Zcash params for code coverage

.github/workflows/ci.yml

@@ -101,6 +101,21 @@ jobs:
         with:
           command: install
           args: cargo-tarpaulin
+
+      - name: Fetch path to Zcash parameters
+        working-directory: ./zcash_proofs
+        run: echo "::set-env name=ZCASH_PARAMS::$(cargo run --release --example get-params-path --features directories)"
+      - name: Cache Zcash parameters
+        id: cache-params
+        uses: actions/cache@v2
+        with:
+          path: ${{ env.ZCASH_PARAMS }}
+          key: ${{ runner.os }}-params
+      - name: Fetch Zcash parameters
+        if: steps.cache-params.outputs.cache-hit != 'true'
+        working-directory: ./zcash_proofs
+        run: cargo run --release --example download-params --features download-params
+
       - name: Generate coverage report
         uses: actions-rs/cargo@v1
         with: