chore: regenerate README (#440)

This PR was generated using Autosynth. 🌈


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

```
2021-04-12 15:38:01,232 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-securitycenter/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-04-12 15:38:03,063 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/ff3a248c-5917-47dd-a982-18af44fc7994/targets

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Author: yoshi-automation

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

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-securitycenter.git",
-        "sha": "0f78855a0984eec570397ed566e2f9681a1f04b7"
+        "sha": "d0480e2644baa0419ddeb3404591dde28e92fb9c"
       }
     },
     {

README.md

@@ -17,7 +17,7 @@ If you are using Maven with [BOM][libraries-bom], add this to your pom.xml file
     <dependency>
       <groupId>com.google.cloud</groupId>
       <artifactId>libraries-bom</artifactId>
-      <version>19.2.1</version>
+      <version>20.0.0</version>
       <type>pom</type>
       <scope>import</scope>
     </dependency>