Add supported engines config to package.json.

Author: Robert Jackson

package.json

@@ -33,5 +33,8 @@
     "execa": "^1.0.0",
     "jest": "^24.8.0",
     "prettier": "^1.17.1"
+  },
+  "engines": {
+    "node": "8.* || 10.* || >= 12.*"
   }
 }