chore: regenerate README (#337)

This PR was generated using Autosynth. 🌈


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

```
2021-06-16 19:34:02,328 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-notification/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-06-16 19:34:03,540 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/e233b738-84cf-4a36-90b3-2f4a50525ea1/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-notification.git",
-        "sha": "ff7a446bcace1806bead32c05b1aa297657f050b"
+        "sha": "d534e0c406dc706c0435807ba96e5d7cfa1e8434"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "2430f8d90ed8a508e8422a3a7191e656d5a6bf53"
+        "sha": "8f76a885deaaf2fe234daeba4a8cc4d1b3de8086"
       }
     }
   ]

README.md

@@ -20,18 +20,18 @@ If you are using Maven, add this to your pom.xml file:
 <dependency>
   <groupId>com.google.cloud</groupId>
   <artifactId>google-cloud-notification</artifactId>
-  <version>0.122.0-beta</version>
+  <version>0.122.1-beta</version>
 </dependency>
 ```
 
 If you are using Gradle without BOM, add this to your dependencies
 ```Groovy
-compile 'com.google.cloud:google-cloud-notification:0.122.0-beta'
+compile 'com.google.cloud:google-cloud-notification:0.122.1-beta'
 ```
 
 If you are using SBT, add this to your dependencies
 ```Scala
-libraryDependencies += "com.google.cloud" % "google-cloud-notification" % "0.122.0-beta"
+libraryDependencies += "com.google.cloud" % "google-cloud-notification" % "0.122.1-beta"
 ```
 
 ## Authentication