chore: regenerate README (#512)

This PR was generated using Autosynth. 🌈


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

```
2021-03-23 15:47:44,466 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-automl/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-03-23 15:47:45,391 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/d11cf570-b0a2-4db9-abe5-c2508fae3edd/targets

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

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

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-automl.git",
-        "sha": "1964fc0e30c2aaaf389d2d9c5061de09f456274b"
+        "sha": "b29c00d75e612ab938786e407e389752f6887bc8"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "8b13da943497f75c5303700bff5aabdd85d939e0"
+        "sha": "c84c8f156e09702e1c8946bfb9746e6f5892cf27"
       }
     }
   ]

README.md

@@ -47,7 +47,7 @@ If you are using Maven without BOM, add this to your dependencies:
 <dependency>
   <groupId>com.google.cloud</groupId>
   <artifactId>google-cloud-automl</artifactId>
-  <version>1.3.6</version>
+  <version>1.4.0</version>
 </dependency>
 <dependency>
   <groupId>com.google.cloud</groupId>