[web templates] fix invalid html in main-no-top template; closes #2174806
Document: cubicweb-docTitle: CubicWeb documentationAuthor: LogilabAbstract: Some base documentation for CubicWeb users and developpersSection: Apps/ProgrammingFormat: HTMLIndex: /usr/share/doc/cubicweb-documentation/index.htmlFiles: /usr/share/doc/cubicweb-documentation/*.html