You have triggered an unhandledRejection, you may have forgotten to catch a Promise rejection:

[IDONKN]

You have triggered an unhandledRejection, you may have forgotten to catch a Promise rejection: 0|front-end | Error: Exited with code 3 0|front-end | at ChildProcess. (/data/front-end/vue2-elm/node_modules/opn/index.js:83:13) 0|front-end | at ChildProcess.g (events.js:291:16) 0|front-end | at emitTwo (events.js:106:13) 0|front-end | at ChildProcess.emit (events.js:191:7) 0|front-end | at maybeClose (internal/child_process.js:877:16) 0|front-end | at Socket. (internal/child_process.js:334:11) 0|front-end | at emitOne (events.js:96:13) 0|front-end | at Socket.emit (events.js:188:7) 0|front-end | at Pipe._handle.close [as _onclose] (net.js:498:12)