RewriteCond %{REQUEST_URI} ^(.*?)\/{2,}(.*?)$
RewriteRule . %1/%2 [L,R=301]
RewriteCond %{THE_REQUEST} //
RewriteRule .* /$0 [R=301,L]
RewriteCond %{THE_REQUEST} /index\.html [NC]
RewriteRule ^index\.html$ / [R=301,L]