DEV: Don't force Ember CLI on proxied requests made by Ember CLI (PR #12909)

Ember CLI server makes requests to the Rails/Unicorn server, so we should exclude these requests from getting the “Ember CLI is required in dev mode” message.

GitHub

The title of this pull request changed from “DEV: Don’t force Ember CLI for proxied requests made by Ember CLI” to "DEV: Don’t force Ember CLI on proxied requests made by Ember CLI