Run only on node 13

Author: rokiyama

.github/workflows/main.yml

@@ -7,7 +7,8 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest]
-        node: [10, 12, 13]
+        # node: [10, 12, 13]
+        node: [13]
     steps:
       - uses: actions/checkout@v1
       - uses: actions/setup-node@v1