onwait should take the core as the 2nd arg

Author: mafintosh

index.js

@@ -664,8 +664,8 @@ module.exports = class Hypercore extends EventEmitter {
       if (this.cache) this.cache.set(index, req)
     } else {
       if (opts && opts.wait === false) return null
-      if (opts && opts.onwait) opts.onwait(index)
-      else if (this.onwait) this.onwait(index)
+      if (opts && opts.onwait) opts.onwait(index, this)
+      else if (this.onwait) this.onwait(index, this)
 
       const activeRequests = (opts && opts.activeRequests) || this.activeRequests