ns2.dnsimple.com has no TXT records.
Question and response
Question
dig ns2.dnsimple.com. TXT
Answer
The response has no answer records.
Authority
dnsimple.com. 3600 SOA ns1.dnsimple.com. admin.dnsimple.com. 1438186505 86400 7200 604800 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0