fix(typescript): Github.plugin is a static method, not an instance method

Author: mamodom

scripts/templates/index.d.ts.tpl

@@ -207,7 +207,7 @@ declare class Github {
     wrap(name: string, callback: (request: (options: Github.HookOptions) => Promise<Github.Response<any>>, options: Github.HookOptions) => void): void
   }
 
-  plugin(plugin: Github.Plugin | [Github.Plugin]): Github
+  static plugin(plugin: Github.Plugin | [Github.Plugin]): Github
 
   registerEndpoints(routes: any): void
 

test/typescript-validate.ts

@@ -77,7 +77,7 @@ export default async function() {
     // add logic before, after, catch errors or replace the request altogether
     return request(options)
   })
-  octokit.plugin((octokit, options) => {
+  Octokit.plugin((octokit, options) => {
     octokit.hook.wrap('request', async (request, options) => {
       const time = Date.now()
       const response = await request(options)