Fix html_basic report template to include Devel::Cover version

coverage.html as generated with version 1.17 always just had `This file was generated by Devel::Cover Version ` (note the trailing space) in the HTML comment at the top of the file. In contrary, the html_minimal and the vim report had the version number at the end of that string.

This commit should fix that so that also the html_basic report lists the generating Devel::Cover version in its comment at the top of coverage.html.