chore: regenerate README (#512)

This PR was generated using Autosynth. 🌈


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

```
2021-01-07 22:21:46,285 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-asset/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-01-07 22:21:47,177 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/5e633bbe-e320-4eef-96af-491fd7f1b14f/targets

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

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

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-asset.git",
-        "sha": "78f2e42f4a30592d2bc7ea43ae2b3bd2129fef1f"
+        "sha": "f5e20bb6a44e78b4949ad802c86109fc885c943c"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "a3e990f3545dc8ccd384a75d20ce9cb185ca6a28"
+        "sha": "67f09bf301083798e7220137723222eb00b8f88a"
       }
     }
   ]

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>2.2.1</version>
+  <version>2.3.0</version>
 </dependency>
 
 ```
@@ -52,12 +52,12 @@ compile 'com.google.cloud:google-cloud-asset'
 ```
 If you are using Gradle without BOM, add this to your dependencies
 ```Groovy
-compile 'com.google.cloud:google-cloud-asset:2.2.1'
+compile 'com.google.cloud:google-cloud-asset:2.3.0'
 ```
 
 If you are using SBT, add this to your dependencies
 ```Scala
-libraryDependencies += "com.google.cloud" % "google-cloud-asset" % "2.2.1"
+libraryDependencies += "com.google.cloud" % "google-cloud-asset" % "2.3.0"
 ```
 
 ## Authentication