Update package path in example code.

I don't have a checkout of `code.google.com/p/go.exp/fsnotify` in my GOPATH, so running the fsnotify test suite fails:

```
$ go test github.com/howeyc/fsnotify
# github.com/howeyc/fsnotify
example_test.go:10:2: cannot find package "code.google.com/p/go.exp/fsnotify" in any of:
	/usr/local/Cellar/go/1.1.1/src/pkg/code.google.com/p/go.exp/fsnotify (from $GOROOT)
	/Users/ph/go/src/code.google.com/p/go.exp/fsnotify (from $GOPATH)
```

This pull request fixes that issue.