Regression in b52c73008a9d67e9ddbb841872dc15cdd3d6ee01.
Thanks Tim Graham for the review.
Backport of 540ae68a5cc6339c72375fad9b04dc48f3af4c93 from master.
Removed the trailing newline from widget attrs.html template.
The solution may be revisited by fixing refs #9198 but not
for Django 1.11.
Thanks Dmitry Ivanchenko for the report and Preston Timmons for advice.