Publish unexpected key in params

[okko]

README states:

Otherwise, you may simply specify Publish as a parameter. If both are provided, the value in lambda_params will take precedence.

If I add Publish to my params:

....
Runtime: 'nodejs4.3',
Publish: true,
Timeout: 3
...

I get:

[20:28:36] Error in plugin 'gulp-awslambda'
Message:
Unexpected key 'Publish' found in params
Details:
domainEmitter: [object Object]
domain: [object Object]
domainThrown: false