chore: regenerate README (#529)

This PR was generated using Autosynth. 🌈


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

```
2021-04-12 14:26:18,291 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-automl/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-04-12 14:26:19,719 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/8df17fc0-fedb-470c-8ab8-744734a935ca/targets

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

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-automl.git",
-        "sha": "0f4a58f5f56d647a2fc0c1ea4db3c82810f6e789"
+        "sha": "721572d7863908c5c39a6b79ea23e5ab2ab46559"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "d9ddac83a22a600dd33854c9d835a4fe52284207"
+        "sha": "0a071b3460344886297a304253bf924aa68ddb7e"
       }
     }
   ]

README.md

@@ -64,7 +64,7 @@ If you are using Maven without BOM, add this to your dependencies:
 
 If you are using Gradle 5.x or later, add this to your dependencies
 ```Groovy
-implementation platform('com.google.cloud:libraries-bom:19.2.1')
+implementation platform('com.google.cloud:libraries-bom:20.0.0')
 
 compile 'com.google.cloud:google-cloud-automl'
 ```