Adds string[] type to Params.follow

According to the docs and my previous experience working with the API you can provide arrays, here the official documentation:
https://developer.twitter.com/en/docs/tweets/filter-realtime/api-reference/post-statuses-filter.html

types/twit/index.d.ts

@@ -263,7 +263,7 @@ declare module 'twit' {
       user_id?: number | string,
       lat?: number,
       long?: number,
-      follow?: boolean | string,
+      follow?: boolean | string | string[],
       include_email?: boolean,
       cursor?: number | string,
       tweet_mode?: string,