rocks: use tag instead of branch.

[moonming]

What this PR does / why we need it:

fix #1872, which not using the right way to install from luarocks.

Pre-submission checklist:

• Did you explain what problem does this PR solve? Or what new features have been added?
• Have you added corresponding test cases?
• Have you modified the corresponding document?
• Is this PR backward compatible?

[nic-chen]

we could remove incubating now.

[moonming]

Apache APISIX was an incubator project until version 1.4.1, we don't have to change the historical version Thanks, Ming Wen Twitter: _WenMing nic-chen <notifications@github.com> 于2020年8月6日周四 上午10:18写道：

…

***@***.**** commented on this pull request. ------------------------------ In rockspec/apisix-0.9-0.rockspec <#2003 (comment)>: > @@ -24,7 +24,7 @@ source = { } description = { - summary = "Apache APISIX is a cloud-native microservices API gateway, delivering the ultimate performance, security, open source and scalable platform for all your APIs and microservices.", + summary = "Apache APISIX(incubating) is a cloud-native microservices API gateway, delivering the ultimate performance, security, open source and scalable platform for all your APIs and microservices.", we could remove incubating now. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#2003 (review)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AGJZBK65VKNF7ALNXKQGQILR7IHHXANCNFSM4PWC5F6Q> .

[nic-chen]

Apache APISIX was an incubator project until version 1.4.1, we don't have to change the historical version Thanks, Ming Wen Twitter: _WenMing nic-chen notifications@github.com 于2020年8月6日周四 上午10:18写道：
…
@.**** commented on this pull request. ------------------------------ In rockspec/apisix-0.9-0.rockspec <#2003 (comment)>: > @@ -24,7 +24,7 @@ source = { } description = { - summary = "Apache APISIX is a cloud-native microservices API gateway, delivering the ultimate performance, security, open source and scalable platform for all your APIs and microservices.", + summary = "Apache APISIX(incubating) is a cloud-native microservices API gateway, delivering the ultimate performance, security, open source and scalable platform for all your APIs and microservices.", we could remove incubating now. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#2003 (review)>, or unsubscribe https://github.com/notifications/unsubscribe-auth/AGJZBK65VKNF7ALNXKQGQILR7IHHXANCNFSM4PWC5F6Q .

ok