"graphcool.yml should have required property 'stage'", but property is there

[marktani]

GraphQL PG: Version 1.3.18 (1.3.18.201)
GC: graphcool/1.0.0-alpha3.3.0 (darwin-x64) node-v8.3.0
GraphQL CLI: 2.8.0

# the name for the service (will be part of the service's HTTP endpoint)
service: first

# the cluster and stage the service is deployed to
stage: ${env:GRAPHCOOL_STAGE}
# cluster: ${env:GRAPHCOOL_CLUSTER}

# the file path pointing to your data model
datamodel: database/datamodel.graphql

# to disable authentication:
# disableAuth: true
secret: ${env:GRAPHCOOL_SECRET}

cluster: local

NODE_ENV="dev"
GRAPHCOOL_STAGE="dev"
GRAPHCOOL_CLUSTER="local"
GRAPHCOOL_ENDPOINT="http://localhost:60001/first/dev"
GRAPHCOOL_SECRET="mysecret123"
APP_SECRET="jwtsecret123"

Reproduction

graphql create my-app # choose node-advanced
cd my-app
graphcool deploy
yarn playground

[marktani]

Update: on 1.3.19, running graphql playground doesn't open the PG at all for me.
Update: on 1.3.21, running graphql playground doesn't open the PG at all for me, either.