chore: regenerate README (#189)

This PR was generated using Autosynth. 🌈


<details><summary>Log from Synthtool</summary>

```
2021-08-11 13:58:54,361 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-pubsublite-kafka/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-08-11 13:58:55,636 synthtool [DEBUG] > Wrote metadata to .github/readme/synth.metadata/synth.metadata.

```
</details>

Full log will be available here:
https://source.cloud.google.com/results/invocations/27ad206e-63d9-49cb-b0f2-bba9d4b1f567/targets

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.github/readme/synth.metadata/synth.metadata

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-pubsublite-kafka.git",
-        "sha": "20ae0ba14d7623741b05825be240edcfc33f3974"
+        "sha": "21f238f883ed2b25e5c19d558f9006c115892abd"
       }
     },
     {

README.md

@@ -22,20 +22,20 @@ If you are using Maven, add this to your pom.xml file:
 <dependency>
   <groupId>com.google.cloud</groupId>
   <artifactId>pubsublite-kafka</artifactId>
-  <version>0.5.1</version>
+  <version>0.6.1</version>
 </dependency>
 ```
 
 If you are using Gradle without BOM, add this to your dependencies
 
 ```Groovy
-compile 'com.google.cloud:pubsublite-kafka:0.5.1'
+compile 'com.google.cloud:pubsublite-kafka:0.6.1'
 ```
 
 If you are using SBT, add this to your dependencies
 
 ```Scala
-libraryDependencies += "com.google.cloud" % "pubsublite-kafka" % "0.5.1"
+libraryDependencies += "com.google.cloud" % "pubsublite-kafka" % "0.6.1"
 ```
 
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