chore: regenerate README (#626)

This PR was generated using Autosynth. 🌈


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

```
2021-08-19 17:56:12,293 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-vision/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-08-19 17:56:14,627 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/1f9ad286-0fcb-43de-ad6a-ee3ef28c6a6a/targets

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

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

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-vision.git",
-        "sha": "c8ff9be1a78a2312c1b2f5a58aafd3ba8834189d"
+        "sha": "18f11ae448607074a1b2199ec62fc15cb5a04c54"
       }
     },
     {

README.md

@@ -19,7 +19,7 @@ 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>20.9.0</version>
+      <version>21.0.0</version>
       <type>pom</type>
       <scope>import</scope>
     </dependency>