dub is building docs of dependencies

[Jedzia]

dmd2-2.083.0, win
minimal dub init
with dub.json:
{
	"description": "A minimal D application.",
	"dependencies": {
		"iz": "~>0.6.23"
	},
	"authors": [
		"Jedzia"
	],
	"copyright": "Copyright © 2018, Jedzia",
	"license": "MIT",
	"name": "testdoc"
}

and `dub build -b docs`

Is it normal that dub builds the docs of dependencies (iz library 
in that case).
And if, how to build only the docs of my own project?