fix: drop node v12 and v14 (#257)

Author: kazupon

.github/workflows/test.yml

@@ -22,7 +22,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest]
-        node: [12, 14, 16]
+        node: [16]
     steps:
       - name: Checkout
         uses: actions/checkout@v2

package.json

@@ -73,7 +73,7 @@
     "vue-template-compiler": "^2.6.11"
   },
   "engines": {
-    "node": ">= 12"
+    "node": ">= 16"
   },
   "files": [
     "types/shims-vue-template-compiler.d.ts",