Update workflow.yml

Signed-off-by: Sora Morimoto <sora@morimoto.io>

Author: smorimoto

.github/workflows/workflow.yml

@@ -10,11 +10,9 @@ jobs:
       fail-fast: false
       matrix:
         os:
-          - macos-10.15
-          # - ubuntu-16.04
-          - ubuntu-18.04
-          - ubuntu-20.04
-          - windows-2019
+          - macos-latest
+          - ubuntu-latest
+          - windows-latest
         ocaml-version:
           - 4.08.1
           - 4.05.0
@@ -25,10 +23,10 @@ jobs:
       - name: Checkout code
         uses: actions/checkout@v2
 
-      - name: Use Node.js 14.x
+      - name: Use Node.js 12.x
         uses: actions/setup-node@v1
         with:
-          node-version: 14.x
+          node-version: 12.x
 
       - name: Install npm packages
         run: yarn --frozen-lockfile