Update chatexchange library

[FelixSFD]

As you might have heard, Stack Exchange will remove OpenID.

Since tunaki/chatexchange is currently using OpenID to connect to chat, we had to release an update. If you don't update, you won't be able to connect to chat after July 25, 2018.

We've moved the project to org.sobotics.*. This is the updated dependency:

<dependency>
  <groupId>org.sobotics</groupId>
  <artifactId>chatexchange</artifactId>
  <version>2.0.0</version>
</dependency>

You'll have to update your import statements. All APIs are still the same, so you don't have to modify the implementation.

If you have issues updating your project, feel free to ask for help in our chatroom.