API not compatible?

[GitPlayB]

Hi there~
I'm a newbie to Netty. I just want to try some example code in the book. BUT unfortunately when I set all the dependencies up, I got some problems that seems to be an API incompatible issue.
I'm using exactly the same vesion of Netty as the author Norman.

<dependency>
    <groupId>io.netty</groupId>
    <artifactId>netty-all</artifactId>
    <version>4.1.12.Final</version>
</dependency>

But I got this when I'm writing the echo server, I found that ServerBootstrap$group() method is deprecated, hence the channel() method and methods after that are all unavailable.

It's really afflictive to someone who are new to this framework. Hopefully I get some help from here!