Update README.md (#1277)

Autogenerated changes after running the `sbt docs/generateReadme`
command of the [zio-sbt-website](https://zio.dev/zio-sbt) plugin.

I will automatically update the README.md file whenever there is new
change for README.md, e.g.
- After each release, I will update the version in the installation
section.
- After any changes to the "docs/index.md" file, I will update the
README.md file accordingly.

Co-authored-by: ZIO Assistant <zio-assistant[bot]@users.noreply.github.com>

README.md

@@ -19,8 +19,8 @@ Kafka has a mature Java client for producing and consuming events, but it has a
 In order to use this library, we need to add the following line in our `build.sbt` file:
 
 ```scala
-libraryDependencies += "dev.zio" %% "zio-kafka"         % "2.7.5"
-libraryDependencies += "dev.zio" %% "zio-kafka-testkit" % "2.7.5" % Test
+libraryDependencies += "dev.zio" %% "zio-kafka"         % "2.8.0"
+libraryDependencies += "dev.zio" %% "zio-kafka-testkit" % "2.8.0" % Test
 ```
 
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