Baidu have not been hacked. Their servers reside inside the great firewall meaning any request from outside China has to traverse the GFW before arriving at Baidu's servers. During traversal of the GFW, the Chinese gov is modifying the Baidu server response with malicious javascript.

Baidu has no say in the matter. They could try and help Github by swapping to only serving their analytics scripts over HTTPS. Even then, this would only help once a large majority of existing websites that use Baidu analytics have updated their website code to point to the HTTPS URL. Until then the attack would probably still continue to work.