Oops: Wrong os

Author: steven nguyen

.github/workflows/ci.yml

@@ -9,7 +9,7 @@ jobs:
     name: tests
     strategy:
       matrix:
-        os: [ubuntu-latest, macos-10.14, windows-latest]
+        os: [ubuntu-18.04, macos-latest, windows-latest]
         channel: [beta, nightly]
       fail-fast: false
     runs-on: ${{ matrix.os }}