chore(dht): add API to allow options in findProvs()

As discussed in: ipfs/js-ipfs#1322 (comment)

License: MIT
Signed-off-by: Pascal Precht <[email protected]>

Author: 0x-r4bbit

SPEC/DHT.md

@@ -39,10 +39,13 @@ A great source of [examples][] can be found in the tests for this API.
 
 ##### `Go` **WIP**
 
-##### `JavaScript` - ipfs.dht.findprovs(hash, [callback])
+##### `JavaScript` - ipfs.dht.findprovs(hash, [options, callback])
 
 Where `hash` is a multihash.
 
+`options` an optional object with the following properties
+  - `timeout` - a maximum timeout in milliseconds
+
 `callback` must follow `function (err, peerInfos) {}` signature, where `err` is an error if the operation was not successful. `peerInfos` is an array of objects of type [PeerInfo](https://github.com/libp2p/js-peer-info)
 
 If no `callback` is passed, a promise is returned.
@@ -51,6 +54,8 @@ If no `callback` is passed, a promise is returned.
 
 ```JavaScript
 ipfs.dht.findprovs(multihash, function (err, peerInfos) {})
+
+ipfs.dht.findprovs(multihash, { timeout: 4000 }, function (err, peerInfos) {})
 ```
 
 A great source of [examples][] can be found in the tests for this API.