Cannot run any queries because of an identity claim with a colon
### Summary

I am getting this error when running Postgraphile as well as appsync console directly. I am using Cognito user pools for Auth

```json
{
    "errorType": "error",
    "errorMessage": "invalid configuration parameter name \"appsync.identity_claims_cognito:username\"",
    "code": "42602",
    "length": 215,
    "name": "error",
    "severity": "ERROR",
    "detail": "Custom parameter names must be two or more simple identifiers separated by dots.",
    "file": "guc.c",
    "line": "8095",
    "routine": "find_option",
    "stack": [
        "error: invalid configuration parameter name \"appsync.identity_claims_cognito:username\"",
        "    at Parser.parseErrorMessage (/opt/nodejs/node_modules/pg-protocol/dist/parser.js:287:98)",
        "    at Parser.handlePacket (/opt/nodejs/node_modules/pg-protocol/dist/parser.js:126:29)",
        "    at Parser.parse (/opt/nodejs/node_modules/pg-protocol/dist/parser.js:39:38)",
        "    at TLSSocket.<anonymous> (/opt/nodejs/node_modules/pg-protocol/dist/index.js:11:42)",
        "    at TLSSocket.emit (events.js:400:28)",
        "    at TLSSocket.emit (domain.js:475:12)",
        "    at addChunk (internal/streams/readable.js:293:12)",
        "    at readableAddChunk (internal/streams/readable.js:267:9)",
        "    at TLSSocket.Readable.push (internal/streams/readable.js:206:10)",
        "    at TLSWrap.onStreamRead (internal/stream_base_commons.js:188:23)"
    ]
}
```

### Steps to reproduce

Create a new project and use a user pool to authenticate

### Expected results

Need this `appsync.identity_claims_cognito:username` to be this `appsync.identity_claims_cognito.username`

### Actual results

Forces a null list back when running a query because of the failure
