I am using El Capitan, so can't say if anything has changed on Sierra.
Is the version of TextWrangler that you have one that was downloaded directly from Bare Bones Software as per my link above, or did you download it from the App Store? The App Store version is different and cannot be used to edit the hosts files:
http://www.barebones.com/support/textwrangler/faqs.html
Scooby is correct that the changes to the hosts file will not be effective until you clear the DNS cache or reboot.