Use ubuntu-18.04 (#188)

driesvints · web-flow · commit e4f48b9eb3d1 · 2021-03-05T21:55:53.000+01:00
diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
@@ -8,7 +8,7 @@ on:
 
 jobs:
   linux_tests:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-18.04
 
     strategy:
       fail-fast: true
