Error: Unknown type: "AWSDateTime"

I'm using AWS AppSync to write my graphql service.
AppSync supports more types out of the box like: AWSDateTime.
But in the apollo vscode plugin I get the following error:
`UnhandledPromiseRejectionWarning: Error: Unknown type: "AWSDateTime".`
Does this plugin not work with AWS or custom types?
Or is this a bug?

Im using version: 1.11.0
And my apollo config looks like this:
```javascript
module.exports = {
client: {
service: {
name: 'ProjectName',
url: 'AWS_APPSYNC_URL',
excludes: ['node_modules/**/*'],
includes: ['src/**/*.graphql'],
},
},
};
```

Start with the Apollo VSCode plugin's schema handling and reproduce the error using the supplied Apollo config, the AWS AppSync service, and a src/**/*.graphql file containing AWSDateTime. Determine whether the plugin accepts AppSync or custom scalar types, and consider the issue done when the unknown-type error no longer occurs for the reported configuration.

Written by the indexing model from the issue text.