chore: regenerate README (#311)

This PR was generated using Autosynth. 🌈


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

```
2020-12-14 20:04:39,063 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-scheduler/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2020-12-14 20:04:39,924 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/eb2b7664-f4e6-45ca-b40f-ccf01521541f/targets

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

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-scheduler.git",
-        "sha": "2c117328910f9881aeada2d75f9433c5a97de40c"
+        "sha": "5555fbc8ca4bae926057a587772c630167df0844"
       }
     },
     {

README.md

@@ -38,7 +38,7 @@ If you are using Maven without BOM, add this to your dependencies:
 <dependency>
   <groupId>com.google.cloud</groupId>
   <artifactId>google-cloud-scheduler</artifactId>
-  <version>1.23.3</version>
+  <version>1.23.4</version>
 </dependency>
 
 ```