chore: regenerate README (#243)

This PR was generated using Autosynth. 🌈


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

```
2021-04-30 18:16:16,534 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-workflows/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-04-30 18:16:17,823 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/7a946217-a32d-4fbd-b489-28c70b1aa200/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": "201bc199974d067485585af561c7974a98eb73c5"
+        "sha": "5ae84a9cca77402b8b1d18372ee9aeb8728cc51a"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "0a071b3460344886297a304253bf924aa68ddb7e"
+        "sha": "06a8cd0ff7e81b05e6c503eab510ec622384caa7"
       }
     }
   ]

java-workflows/README.md

@@ -20,19 +20,19 @@ If you are using Maven, add this to your pom.xml file:
 <dependency>
   <groupId>com.google.cloud</groupId>
   <artifactId>google-cloud-workflows</artifactId>
-  <version>0.3.1</version>
+  <version>0.4.0</version>
 </dependency>
 
 ```
 
 If you are using Gradle without BOM, add this to your dependencies
 ```Groovy
-compile 'com.google.cloud:google-cloud-workflows:0.3.1'
+compile 'com.google.cloud:google-cloud-workflows:0.4.0'
 ```
 
 If you are using SBT, add this to your dependencies
 ```Scala
-libraryDependencies += "com.google.cloud" % "google-cloud-workflows" % "0.3.1"
+libraryDependencies += "com.google.cloud" % "google-cloud-workflows" % "0.4.0"
 ```
 
 ## Authentication