Add cargo-audit CI

Author: Vasilii Novikov

.github/workflows/cargo-audit.yml

@@ -0,0 +1,12 @@
+name: Security audit
+on:
+  schedule:
+    - cron: '4 0 * * Sat'  # 4:00 each Saturday
+jobs:
+  audit:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v1
+      - uses: actions-rs/audit-check@v1
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}