Pass logger to middleware.Log
Pass logger to middleware.Log

Should fix:
```
2018/07/23 20:29:49 http: panic serving 10.244.204.241:34716: runtime error: invalid memory address or nil pointer dereference
goroutine 1169 [running]:
net/http.(*conn).serve.func1(0xc420739a40)
/usr/local/go/src/net/http/server.go:1726 +0xd0
panic(0x17d5200, 0x2a7f5e0)
/usr/local/go/src/runtime/panic.go:502 +0x229
github.com/weaveworks/scope/vendor/github.com/weaveworks/common/middleware.Log.Wrap.func1(0x1dc60e0, 0xc4215e7a40, 0xc4202cee00)
/go/src/github.com/weaveworks/scope/vendor/github.com/weaveworks/common/middleware/logging.go:40 +0x3c7
[...]
```

weaveworks/scope,weaveworks/scope,weaveworks/scope,weaveworks/scope,weaveworks/scope,weaveworks/scope