bugfix: used tag v0.1.0 for luarocks. (#36)

diff --git a/rockspec/skywalking-nginx-lua-0.1-0.rockspec b/rockspec/skywalking-nginx-lua-0.1-0.rockspec
index f02a681..cab0eea 100644
--- a/rockspec/skywalking-nginx-lua-0.1-0.rockspec
+++ b/rockspec/skywalking-nginx-lua-0.1-0.rockspec
@@ -2,7 +2,7 @@
 version = "0.1-0"
 source = {
    url = "git://github.com/apache/skywalking-nginx-lua",
-   branch = "master",
+   tag = "v0.1.0",
 }
 
 description = {