chore: only run GitHub actions on Node 12 / Linux

Author: beeman

.github/workflows/test.yml

@@ -11,20 +11,16 @@ on:
 
 jobs:
   lint-and-test:
-    name: Test on node ${{ matrix.node-version }} and ${{ matrix.os }}
-    runs-on: ${{ matrix.os }}
-    strategy:
-      matrix:
-        node-version: [10, 12]
-        os: [ubuntu-latest, windows-latest, macOS-latest]
+    name: Test on node 12 and ubuntu-latest
+    runs-on: ubuntu-latest
 
     steps:
       - uses: actions/checkout@v1
         with:
           fetch-depth: 1
       - uses: actions/setup-node@v1
         with:
-          node-version: ${{ matrix.node-version }}
+          node-version: 12
       - run: yarn
       - run: yarn lint
       - run: yarn build