use pm2 on heroku

Procfile

@@ -1 +1 @@
-web: pm2 start server.js
+web: npm run prod

ecosystem.config.js

@@ -0,0 +1,16 @@
+require('dotenv').config();
+
+module.exports = {
+  apps: [
+    {
+      name: 'Server',
+      script: 'server.js',
+
+      // Options reference: https://pm2.io/doc/en/runtime/reference/ecosystem-file/
+      instances: 2,
+      autorestart: true,
+      watch: false,
+      max_memory_restart: '1G'
+    }
+  ]
+};

package.json

@@ -23,7 +23,8 @@
     "start": "cross-env NODE_ENV=development nodemon server.js",
     "debug": "cross-env NODE_ENV=development nodemon --debug server.js",
     "test": "cross-env NODE_ENV=test babel-tape-runner test/test-*.js",
-    "pretest": "eslint ."
+    "pretest": "eslint .",
+    "prod": "pm2-runtime start ecosystem.config.js --env production"
   },
   "dependencies": {
     "body-parser": "~1.18.3",