fix(typescript): export Webhooks explicitly

This is how we do it in @octokit/rest. I don’t know if that’s the right way to do it, but this change was necessary in order to get probot/probot#832 to work

Author: gr2m

scripts/generate-types.js

@@ -51,23 +51,26 @@ export namespace Webhooks {
     host?: string
     url?: string
   }
-  export class Webhooks {
-    constructor (options: Options)
+}
 
-    public on (event: 'error', callback: (event: Error) => void): void
-    public on (event: '*' | string | string[], callback: (event: Webhooks.WebhookEvent<any>) => void): void
-    public on (event: '*' | string | string[], callback: (event: Webhooks.WebhookEvent<any>) => Promise<void>): void
-    ${signatures.join('\n')}
+export class Webhooks {
+  constructor (options: Options)
 
-    public sign (data: any): string
-    public verify (eventPayload: any, signature: string): boolean
-    public verifyAndReceive (options: { id: string, name: string, payload: any, signature: string }): Promise<void>
-    public receive (options: { id: string, name: string, payload: any }): Promise<void>
-    public removeListener (event: string | string[], callback: (event: Webhooks.WebhookEvent<any>) => void): void
-    public removeListener (event: string | string[], callback: (event: Webhooks.WebhookEvent<any>) => Promise<void>): void
-    public middleware (request: http.ClientRequest, response: http.ServerResponse, next: (err?: any) => void): (request: http.IncomingMessage, response: http.ServerResponse) => void
-  }
+  public on (event: 'error', callback: (event: Error) => void): void
+  public on (event: '*' | string | string[], callback: (event: Webhooks.WebhookEvent<any>) => void): void
+  public on (event: '*' | string | string[], callback: (event: Webhooks.WebhookEvent<any>) => Promise<void>): void
+  ${signatures.join('\n')}
+
+  public sign (data: any): string
+  public verify (eventPayload: any, signature: string): boolean
+  public verifyAndReceive (options: { id: string, name: string, payload: any, signature: string }): Promise<void>
+  public receive (options: { id: string, name: string, payload: any }): Promise<void>
+  public removeListener (event: string | string[], callback: (event: Webhooks.WebhookEvent<any>) => void): void
+  public removeListener (event: string | string[], callback: (event: Webhooks.WebhookEvent<any>) => Promise<void>): void
+  public middleware (request: http.ClientRequest, response: http.ServerResponse, next: (err?: any) => void): (request: http.IncomingMessage, response: http.ServerResponse) => void
 }
+
+export = Webhooks
 `
 
 const filepath = 'index.d.ts'