chore: regenerate README (#266)

This PR was generated using Autosynth. 🌈


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

```
2021-05-26 15:22:09,754 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-workflows/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-05-26 15:22:10,947 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/e71c01f5-2699-4770-ad4b-df1e71f53239/targets

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java-workflows/.github/readme/synth.metadata/synth.metadata

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-workflows.git",
-        "sha": "c3fb06c73388e857cedeca068714a9c2ec5f2bb9"
+        "sha": "a901f95055c13e57a8af9f71f05a54ffb21e2beb"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "bf148334fb9ee928d4c302d2aa32eb61252808d1"
+        "sha": "1778de119522ea9c9b18763c2a4577e22a60433c"
       }
     }
   ]

java-workflows/README.md

@@ -20,7 +20,7 @@ If you are using Maven, add this to your pom.xml file:
 <dependency>
   <groupId>com.google.cloud</groupId>
   <artifactId>google-cloud-workflows</artifactId>
-  <version>0.4.0</version>
+  <version>0.4.2</version>
 </dependency>
 
 ```