fix #1206

Limit the node version to be used in package.json.
This prevents heroku one click deployment to use unsupported nodeJS.

Signed-off-by: t.goto <tomoyan777@gmail.com>

Author: tomgoto

package.json

@@ -193,7 +193,7 @@
     "utf-8-validate": "~5.0.1"
   },
   "engines": {
-    "node": ">=8.0.0"
+    "node": ">=8.0.0 <12.0.0"
   },
   "maintainers": [
     {