Run audit if deps changed, on merge requests and scheduled

.github/workflows/audit.yml

@@ -0,0 +1,31 @@
+name: Security audit
+on:
+  schedule:
+    - cron: '0 1 * * *'
+  push:
+    paths:
+      - '**/Cargo.toml'
+      - '**/Cargo.lock'
+  pull_request:
+
+jobs:
+  security_audit:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v1
+
+      - name: Cache cargo registry
+        uses: actions/cache@v1
+        with:
+          path: /usr/share/rust/.cargo/registry
+          key: ${{ runner.os }}-cargo-registry
+
+      - name: Cache cargo index
+        uses: actions/cache@v1
+        with:
+          path: /usr/share/rust/.cargo/git
+          key: ${{ runner.os }}-cargo-index
+
+      - uses: actions-rs/audit-check@v1
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}