Unnown token spread operator on Heroku, locally working
Spread wasn't supported in node until 8.2.1 try updating your node version
You need to update your node version, node version 8.1.1 not support this operator.
The reason I was asking you about the Node version on my comment, was because spread operator introduced on node 8.2.1, so if Heroku uses version 8.1.1 as you've told me on your comment, then this should cause the error.