chore: regenerate README (#118)

This PR was generated using Autosynth. 🌈


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

```
2021-06-14 16:30:23,045 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-channel/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-06-14 16:30:25,866 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/7731b8cb-32bf-4659-9241-1d9590cb96fd/targets

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Author: yoshi-automation

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

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-channel.git",
-        "sha": "56aa1ea72582a2e7d68a970922ab6cf6238c1cc2"
+        "sha": "a7cc927e7b18a16f6bd3e35044dedbe4922fffa7"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "811d20bc0b00c09773dfc74ac2baaf1286e943b7"
+        "sha": "41ccd8cd13ec31f4fb839cf8182aea3c7156e19d"
       }
     }
   ]

README.md

@@ -24,12 +24,12 @@ If you are using Maven, add this to your pom.xml file:
 
 If you are using Gradle without BOM, add this to your dependencies
 ```Groovy
-compile 'com.google.cloud:google-cloud-channel:2.2.0'
+compile 'com.google.cloud:google-cloud-channel:2.2.1'
 ```
 
 If you are using SBT, add this to your dependencies
 ```Scala
-libraryDependencies += "com.google.cloud" % "google-cloud-channel" % "2.2.0"
+libraryDependencies += "com.google.cloud" % "google-cloud-channel" % "2.2.1"
 ```
 
 ## Authentication