chore: require node14+ (#404)

* chore: require node14+

* chore(ci): drop nodejs12 & add nodejs18

Author: yoshinorin

.github/workflows/tester.yml

@@ -8,7 +8,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, windows-latest, macos-latest]
-        node-version: ['12.x', '14.x', '16.x']
+        node-version: ['14.x', '16.x', '18.x']
       fail-fast: false
     steps:
       - uses: actions/checkout@v3

package.json

@@ -61,6 +61,6 @@
     "sinon": "^14.0.0"
   },
   "engines": {
-    "node": ">=12.13.0"
+    "node": ">=14"
   }
 }