ci: update runner

.github/workflows/ci.yml

@@ -12,19 +12,14 @@ defaults:
 
 jobs:
   ubuntu:
-    runs-on: ${{ matrix.os }}
-    strategy:
-      matrix:
-        os: [ubuntu-16.04, ubuntu-18.04]
-        node-version: [10]
+    runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
       - run: sudo apt-get install shellcheck -y
       - run: ./tests/shellcheck.sh
-      - name: Use Node.js ${{ matrix.node-version }}
-        uses: actions/setup-node@v1
+      - uses: actions/setup-node@v2
         with:
-          node-version: ${{ matrix.node-version }}
+          node-version: "13"
       - run: npm install -g bats
       - run: ./dotbare finit -u https://github.com/kazhala/dotfiles.git
       - run: bats tests