ci: drop testing for node 13

Author: icelam

.github/workflows/ci.yml

@@ -17,7 +17,7 @@ jobs:
     runs-on: ubuntu-18.04
     strategy:
       matrix:
-        node-version: [12.x, 13.x, 14.x]
+        node-version: [12.x, 14.x]
     env:
       HUSKY: 0
     steps: