fix: appsync_resolver example
fix: appsync_resolver example

Prevents the following error:

```
Error: BadRequestException: Invalid data source name given, must match pattern [_A-Za-z][_0-9A-Za-z]*
```
kjmkznr/terraform-provider-aws,terraform-providers/terraform-provider-aws,terraform-providers/terraform-provider-aws,kjmkznr/terraform-provider-aws,kjmkznr/terraform-provider-aws,kjmkznr/terraform-provider-aws,terraform-providers/terraform-provider-aws,terraform-providers/terraform-provider-aws