CI: use cargo-audit v0.20 (#170)

Author: tarcieri

.github/workflows/security-audit.yml

@@ -18,7 +18,7 @@ jobs:
         uses: actions/cache@v3
         with:
           path: ~/.cargo/bin
-          key: ${{ runner.os }}-cargo-audit-v0.12
+          key: ${{ runner.os }}-cargo-audit-v0.20
       - uses: actions-rs/audit-check@v1
         with:
           token: ${{ secrets.GITHUB_TOKEN }}