chore: regenerate README (#109)

This PR was generated using Autosynth. 🌈


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

```
2021-06-03 15:26:24,662 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-channel/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-06-03 15:26:25,872 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/791c42db-12ce-47bd-ba0b-c3e7035be46f/targets

- [ ] To automatically regenerate this PR, check this box. (May take up to 24 hours.)

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

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-channel.git",
-        "sha": "a72ef86acddef85f11db181afd1a39414fa4867f"
+        "sha": "56aa1ea72582a2e7d68a970922ab6cf6238c1cc2"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "a2de127f90799cd5bace653b1dcc5dd2ca8b19c9"
+        "sha": "811d20bc0b00c09773dfc74ac2baaf1286e943b7"
       }
     }
   ]

README.md

@@ -17,19 +17,19 @@ If you are using Maven, add this to your pom.xml file:
 <dependency>
   <groupId>com.google.cloud</groupId>
   <artifactId>google-cloud-channel</artifactId>
-  <version>2.1.1</version>
+  <version>2.2.0</version>
 </dependency>
 
 ```
 
 If you are using Gradle without BOM, add this to your dependencies
 ```Groovy
-compile 'com.google.cloud:google-cloud-channel:2.1.1'
+compile 'com.google.cloud:google-cloud-channel:2.2.0'
 ```
 
 If you are using SBT, add this to your dependencies
 ```Scala
-libraryDependencies += "com.google.cloud" % "google-cloud-channel" % "2.1.1"
+libraryDependencies += "com.google.cloud" % "google-cloud-channel" % "2.2.0"
 ```
 
 ## Authentication