Update node engine to 18.x

Author: albertosantini

.github/workflows/ci.yml

@@ -9,7 +9,7 @@ jobs:
 
     strategy:
       matrix:
-        node-version: [10.x, 12.x]
+        node-version: [18.x]
 
     steps:
     - uses: actions/checkout@v1

package.json

@@ -12,7 +12,7 @@
     "author": "Alberto Santini",
     "license": "MIT",
     "engines": {
-        "node": ">=8.x"
+        "node": ">=18.x"
     },
     "scripts": {
         "test": "npm run lint && npm run tape && npm run benchmark",