docs: update pubsub func signatures on the readme

Author: daviddias

README.md

@@ -235,8 +235,8 @@ $ ipfs config --json API.HTTPHeaders.Access-Control-Allow-Methods "[\"PUT\", \"P
   - [`ipfs.dht.put()`](https://github.com/ipfs/interface-ipfs-core/tree/master/SPEC/DHT.md#put)
   
 - [pubsub](https://github.com/ipfs/interface-ipfs-core/tree/master/SPEC/PUBSUB.md)
-  - [`ipfs.pubsub.subscribe(topic, options, handler, callback)`](https://github.com/ipfs/interface-ipfs-core/tree/master/SPEC/PUBSUB.md#pubsubsubscribe)
-  - [`ipfs.pubsub.unsubscribe(topic, handler)`](https://github.com/ipfs/interface-ipfs-core/tree/master/SPEC/PUBSUB.md#pubsubunsubscribe)
+  - [`ipfs.pubsub.subscribe(topic, handler, options, callback)`](https://github.com/ipfs/interface-ipfs-core/tree/master/SPEC/PUBSUB.md#pubsubsubscribe)
+  - [`ipfs.pubsub.unsubscribe(topic, handler, callback)`](https://github.com/ipfs/interface-ipfs-core/tree/master/SPEC/PUBSUB.md#pubsubunsubscribe)
   - [`ipfs.pubsub.publish(topic, data, callback)`](https://github.com/ipfs/interface-ipfs-core/tree/master/SPEC/PUBSUB.md#pubsubpublish)
   - [`ipfs.pubsub.ls(topic, callback)`](https://github.com/ipfs/interface-ipfs-core/tree/master/SPEC/PUBSUB.md#pubsubls)
   - [`ipfs.pubsub.peers(topic, callback)`](https://github.com/ipfs/interface-ipfs-core/tree/master/SPEC/PUBSUB.md#pubsubpeers)