Fix broken link in README.md
It looks like `github.com/whyrusleeping/go-smux-mplex` was renamed to `github.com/whyrusleeping/go-smux-multiplex`.
@@ -141,7 +141,7 @@ List of packages currently in existence for libp2p:
| **Stream Muxers** |
| [`go-stream-muxer`](//github.com/libp2p/go-stream-muxer) | [![Travis CI](https://travis-ci.com/libp2p/go-stream-muxer.svg?branch=master)](https://travis-ci.com/libp2p/go-stream-muxer) | [![codecov](https://codecov.io/gh/libp2p/go-stream-muxer/branch/master/graph/badge.svg)](https://codecov.io/gh/libp2p/go-stream-muxer) | interfaces |
| [`go-smux-yamux`](//github.com/whyrusleeping/go-smux-yamux) | [![Travis CI](https://travis-ci.com/whyrusleeping/go-smux-yamux.svg?branch=master)](https://travis-ci.com/whyrusleeping/go-smux-yamux) | [![codecov](https://codecov.io/gh/whyrusleeping/go-smux-yamux/branch/master/graph/badge.svg)](https://codecov.io/gh/whyrusleeping/go-smux-yamux) | YAMUX stream multiplexer |
-| [`go-smux-mplex`](//github.com/whyrusleeping/go-smux-mplex) | [![Travis CI](https://travis-ci.com/whyrusleeping/go-smux-mplex.svg?branch=master)](https://travis-ci.com/whyrusleeping/go-smux-mplex) | [![codecov](https://codecov.io/gh/whyrusleeping/go-smux-mplex/branch/master/graph/badge.svg)](https://codecov.io/gh/whyrusleeping/go-smux-mplex) | MPLEX stream multiplexer |
+| [`go-smux-multiplex`](//github.com/whyrusleeping/go-smux-multiplex) | [![Travis CI](https://travis-ci.com/whyrusleeping/go-smux-multiplex.svg?branch=master)](https://travis-ci.com/whyrusleeping/go-smux-multiplex) | [![codecov](https://codecov.io/gh/whyrusleeping/go-smux-multiplex/branch/master/graph/badge.svg)](https://codecov.io/gh/whyrusleeping/go-smux-multiplex) | MPLEX stream multiplexer |
| **NAT Traversal** |
| [`go-libp2p-nat`](//github.com/libp2p/go-libp2p-nat) | [![Travis CI](https://travis-ci.com/libp2p/go-libp2p-nat.svg?branch=master)](https://travis-ci.com/libp2p/go-libp2p-nat) | [![codecov](https://codecov.io/gh/libp2p/go-libp2p-nat/branch/master/graph/badge.svg)](https://codecov.io/gh/libp2p/go-libp2p-nat) | |
| **Peerstore** |
