fix: template ungrouped api links

Author: alovn

gen/template/markdown/group_index.tpl

@@ -12,5 +12,5 @@ version: _@{{.Version}}_
 {{range $k,$v := .Groups}}
 {{add $k 1}}. [{{$v.Title}}](./apis-{{$v.Group}}.md)
 {{range $k2,$api := $v.Apis}}
-    {{add $k 1}}.{{add $k2 1}}. [{{$api.Title}}](./apis-{{$api.Group}}.md#{{add $k2 1}}-{{$api.Title}}) {{- if $api.Deprecated}}(Deprecated){{end}}
+    {{add $k 1}}.{{add $k2 1}}. [{{$api.Title}}](./apis-{{$v.Group}}.md#{{add $k2 1}}-{{$api.Title}}) {{- if $api.Deprecated}}(Deprecated){{end}}
 {{end}}{{end}}