Fix CI job: Add apt update (#62)

Author: AlfioEmanueleFresta

.github/workflows/rust.yml

@@ -11,6 +11,8 @@ jobs:
       - uses: actions/checkout@v2
       - name: Checkout submodules
         run: git submodule update --init --recursive
+      - name: Update apt cache
+        run: sudo apt-get update
       - name: Install system dependencies
         run: sudo apt-get install libudev-dev libdbus-1-dev libsodium-dev
       - name: Build