chore: regenerate README (#371)

This PR was generated using Autosynth. 🌈


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

```
2021-04-12 16:07:09,496 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-dns/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-04-12 16:07:10,740 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/f2f8eae4-e83b-48ba-a139-85fd55d7b739/targets

- [ ] To automatically regenerate this PR, check this box. (May take up to 24 hours.)

Author: yoshi-automation

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

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-dns.git",
-        "sha": "9af16280b377daf4460f29e8e652788985e1d7e4"
+        "sha": "e211bd9c029535f7961583caff5ef1857cccb452"
       }
     },
     {

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>