Refs #10602.  Fixed the bug.
Refs #10602.  Modified sub bullet sign from * to -.

As Martyn's suggestion.  Though it does not seems to change any format
in the generated html file.
On the other hand, the previously reported warning was fixed by last
commit (http://builds.mantidproject.org/job/develop_clean/505/)
Merge branch 'bugfix/10602_fix_sphinx_warning'