chore: regenerate README (#185)

This PR was generated using Autosynth. 🌈


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

```
2021-05-31 18:11:20,341 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-security-private-ca/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-05-31 18:11:22,080 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/d0fa9f35-3182-4c46-bdf0-6c85bf6e9561/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-security-private-ca.git",
-        "sha": "a79eaa92f41727e63e67fbba22ae3a487f4dbbe4"
+        "sha": "b1fa5ad91761b1ea5c3c018d270ec0419140a5d4"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "ff6b759fcb58f216f62b48d5be0bb85fafbc3bb2"
+        "sha": "c3e41da0fa256ad7f6b4bc76b9d069dedecdfef4"
       }
     }
   ]

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-security-private-ca</artifactId>
-  <version>0.3.0</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-security-private-ca:0.3.0'
+compile 'com.google.cloud:google-cloud-security-private-ca:0.4.0'
 ```
 
 If you are using SBT, add this to your dependencies
 ```Scala
-libraryDependencies += "com.google.cloud" % "google-cloud-security-private-ca" % "0.3.0"
+libraryDependencies += "com.google.cloud" % "google-cloud-security-private-ca" % "0.4.0"
 ```
 
 ## Authentication