Fix the Sphinx html_last_updated_fmt for Python3.
The html_last_updated_fmt option is interpeted as a
byte string in python3, causing Sphinx build to break.
This patch makes it utf-8 string.
Change-Id: I24f83aa15cd4301aac9a7a941fe7d4c1e497c46e
Closes-Bug: #1659390
Signed-off-by: ashish.billore <ashish.billore@gmail.com>
9dc4c8704e