cron.yml in einvoice-1.2.16

- old
+ new

@@ -2,10 +2,10 @@
 on:
   schedule:
     - cron: 0 0 * * *
 jobs:
   build:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-18.04
     steps:
     - uses: actions/checkout@v2
     - uses: actions/setup-ruby@v1
     - name: bundle and run rake update
       run: |