Memory leak when using Socket.readString

The following code results in a big amount of memory being allocated by the process that is not being released.
After 20k connections, the used memory of the process is more than 100MB. After removing the call to `readString`, the memory usage does not increase anymore. I tested this with BlueSocket 1.0.52.

```
var i = 0
while true {
let socket = try Socket.create()
try! socket.connect(to: "localhost", port: 31337)
let serviceResponse = try! socket.readString()!

i += 1
print(i, String(describing: serviceResponse))
Thread.sleep(forTimeInterval: 0.001)
}
```

The socket connects to a service that first responds with "foobar" and then closes the connection.

The code for reproducing this can be found in the repository https://github.com/johannes87/TestBlueSocketMemoryLeak

The target `TestService` inside the Xcode project is the "foobar" service mentioned above.