fix: functions invoke reference slug.

spec/common-client-libs-sections.json

@@ -730,7 +730,7 @@
       {
         "id": "invoke",
         "title": "Invoke a function",
-        "slug": "auth-admin-invoke",
+        "slug": "functions-invoke",
         "product": "functions",
         "type": "function",
         "libs": ["js", "js_v1", "dart", "dart_v0"]

spec/common-client-libs.yml

@@ -361,7 +361,7 @@ functions:
 
   - id: invoke
     title: invoke()
-    slug: auth-admin-invoke
+    slug: functions-invoke
     product: 'functions'
 
   - id: stream