svg-sanitizer Bypasses Attribute Sanitization

Problem The sanitization logic at https://github.com/darylldoyle/svg-sanitizer/blob/0.21.0/src/Sanitizer.phpL454-L481 only searches for lower-case attribute names e.g. xlink:href instead of xlink:HrEf, which allows to by-pass the isHrefSafeValue check. As a result this allows cross-site scripting...