Bump github.com/libp2p/go-libp2p in /example/01-echo (#198)

Bumps [github.com/libp2p/go-libp2p](https://github.com/libp2p/go-libp2p) from 0.8.1 to 0.18.0.
- [Release notes](https://github.com/libp2p/go-libp2p/releases)
- [Commits](https://github.com/libp2p/go-libp2p/compare/v0.8.1...v0.18.0)

---
updated-dependencies:
- dependency-name: github.com/libp2p/go-libp2p
  dependency-type: direct:production
...

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example/01-echo/go.mod

@@ -1,12 +1,11 @@
 module github.com/libp2p/go-libp2p-examples
 
 require (
-	github.com/gogo/protobuf v1.3.2 // indirect
+	github.com/ipfs/go-log v1.0.5
-	github.com/ipfs/go-log v1.0.3
+	github.com/libp2p/go-libp2p v0.18.0
-	github.com/libp2p/go-libp2p v0.8.1
+	github.com/libp2p/go-libp2p-core v0.14.0
-	github.com/libp2p/go-libp2p-core v0.5.1
+	github.com/libp2p/go-libp2p-noise v0.3.0
-	github.com/libp2p/go-libp2p-noise v0.1.2
+	github.com/multiformats/go-multiaddr v0.5.0
-	github.com/multiformats/go-multiaddr v0.2.1
 	github.com/whyrusleeping/go-logging v0.0.1
 )