When the DNT request header value is set to 1, the response header from Piwik is set to 1

Example request header:
Accept:image/webp,image/*,/;q=0.8
Accept-Encoding:gzip, deflate, sdch, br
Accept-Language:en-US,en;q=0.8
Cache-Control:no-cache
Connection:keep-alive
DNT:1
Host:myhost.co.uk
Pragma:no-cache
Referer:hmyhost.co.uk/
User-Agent:Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/52.0.2743.82 Safari/537.36

Example response header:
Connection:keep-alive
Content-Length:0
Content-Type:text/html; charset=UTF-8
Date:Wed, 17 Aug 2016 13:29:20 GMT
P3P:CP='OTI DSP COR NID STP UNI OTPa OUR'
Strict-Transport-Security:max-age=63072000; includeSubdomains; preload
Tk:1

1 is not a valid value for Tk see here for more information https://www.w3.org/2011/tracking-protection/drafts/tracking-dnt.html#TSV-defn

Tk should be N when DNT is set