bug: The download page link in the release page is invalid

[idbeta]

Issue description

download page link to http://apisix.apache.org/downloads/ which is 404 now.

[membphis]

where did you get this link?

[idbeta]

where did you get this link?

https://github.com/apache/apisix/releases/tag/2.0

[moonming]

will fix in apache/apisix-website#81