Deprecation warning from Serverless Variables Resolver when deploying to GCP using serverless template

**Describe the bug**
```
Serverless: Deprecation warning: Variables resolver reports following resolution errors:
- Cannot resolve variable at "provider.environment.CUBEJS_APP": Value not found at "self" source,
- Cannot resolve variable at "functions.cubejsProcess.events.0.event.resource": Value not found at "self" source
From a next major this will be communicated with a thrown error.
Set "variablesResolutionMode: 20210326" in your service config, to adapt to new behavior now
More Info: https://www.serverless.com/framework/docs/deprecations/#NEW_VARIABLES_RESOLVER
```

**To Reproduce**
Steps to reproduce the behavior:
1. npm install -g serverless
2. npx cubejs-cli create -d bigquery -t serverless-google
3. serverless deploy -v
4. See warnings

**Expected behavior**
Should use self variable fine

**Version:**
0.27