update perspective models docs link (#2844)

src/core/client/admin/routes/Configure/sections/Moderation/PerspectiveConfig.tsx

@@ -156,7 +156,7 @@ const PerspectiveConfig: FunctionComponent<Props> = ({ disabled }) => {
             externalLink={
               <ExternalLink
                 href={
-                  "https://github.com/conversationai/perspectiveapi/blob/master/api_reference.md#models"
+                  "https://github.com/conversationai/perspectiveapi/blob/master/2-api/models.md"
                 }
               />
             }

src/core/client/admin/test/configure/__snapshots__/moderation.spec.tsx.snap

@@ -760,7 +760,7 @@ comment is toxic, according to Perspective API. By default the threshold is set
 You can find out more about model choices 
                       <a
                         className="ExternalLink-root"
-                        href="https://github.com/conversationai/perspectiveapi/blob/master/api_reference.md#models"
+                        href="https://github.com/conversationai/perspectiveapi/blob/master/2-api/models.md"
                         rel="noopener noreferrer"
                         target="_blank"
                       >