Changing default extension "md" to "zkmd" doesn't work

[sysoeviy]

I want to change the default extention to "zkmd". But unfortunately it doesn't work. In sublime_zk.sublime-settings i wrote:

{
	// links like "[[199901012359]] and note title" instead of "[[199901012359]]"
	"color_scheme": "Packages/sublime_zk/Monokai Extended-zk.tmTheme",
	"insert_links_with_titles": true,
	// The preferred markdown extension    
	"markdown_extension": ".zkmd",
	"extensions":
	[
		"zkmd"	
	]
}

Even after this, when i type "[[" the plugin sublime_zk shows me only references to *.md files.

I use: windows 10 with the latest updates;
SublimeText 3: Build 3211.