chore: regenerate README (#483)

This PR was generated using Autosynth. 🌈


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

```
2020-12-14 19:58:24,425 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-asset/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2020-12-14 19:58:25,345 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/fe05006d-3115-4ec2-ba6a-3068172bafb5/targets

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

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-asset.git",
-        "sha": "70bba471f090d98693fec7e687d3dcc0b464d986"
+        "sha": "c26e59fef7a24c39f50796204722b193c2bdefb4"
       }
     },
     {

README.md

@@ -39,7 +39,7 @@ If you are using Maven without BOM, add this to your dependencies:
 <dependency>
   <groupId>com.google.cloud</groupId>
   <artifactId>google-cloud-asset</artifactId>
-  <version>2.1.1</version>
+  <version>2.2.0</version>
 </dependency>
 
 ```