show UnhandledPromiseRejectionWarning to console

lib/crowi/dev.js

@@ -19,10 +19,16 @@ class CrowiDev {
   }
 
   init() {
+    this.initPromiseRejectionWarningHandler();
     this.initSwig();
     this.hackLRWebSocketServer();
   }
 
+  initPromiseRejectionWarningHandler() {
+    // https://qiita.com/syuilo/items/0800d7e44e93203c7285
+    process.on('unhandledRejection', console.dir);
+  }
+
   initSwig() {
     swig.setDefaults({ cache: false });
   }