chore: regenerate README (#320)

This PR was generated using Autosynth. 🌈


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

```
2020-11-02 20:48:18,048 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-containeranalysis/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working directory clean
2020-11-02 20:48:19,000 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/457cf712-da1e-4bd1-bd20-b8a557203599/targets

- [ ] To automatically regenerate this PR, check this box.

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

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-containeranalysis.git",
-        "sha": "e17cece5d3ad0dd3d6bfda25a9c48bed46f46033"
+        "sha": "3bd3aee9e5f38d818bab27fddf920f3c722b4851"
       }
     },
     {

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-containeranalysis</artifactId>
-  <version>1.2.1</version>
+  <version>1.2.4</version>
 </dependency>
 
 ```