Update httpd dependency
Update httpd dependency

httpd references a commit which is no longer accessible
after the move of the ASSF repos from git.apache.org to
github.

We update to cef6805cb18886c5454a38f3501c5e3c990c0b3d,
which should be equivalent.

Signed-off-by: Otto van der Schaaf <f82e1104fcd8bfffc72e7185709f7902b0b97ebf@we-amp.com>

pagespeed/mod_pagespeed,pagespeed/mod_pagespeed,pagespeed/mod_pagespeed,pagespeed/mod_pagespeed,pagespeed/mod_pagespeed,pagespeed/mod_pagespeed,pagespeed/mod_pagespeed