chore: regenerate README (#431)

This PR was generated using Autosynth. 🌈


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

```
2021-04-12 16:09:59,659 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-language/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-04-12 16:10:00,936 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/d9f8a715-6b35-4439-b043-c92253dd01d1/targets

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

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-language.git",
-        "sha": "c05d27ac12712b7f3233e651ab8be8d4f3871831"
+        "sha": "0e30b8d342bc73362ece5e9b58fcd01fa920d58e"
       }
     },
     {

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>