chore: regenerate README (#428)

This PR was generated using Autosynth. 🌈


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

```
2021-05-17 20:58:51,777 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-datastore/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-05-17 20:58:53,146 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/765f04fe-d4f4-4558-808a-89f065eb0b37/targets

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

Author: yoshi-automation

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

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-datastore.git",
-        "sha": "4efd9b359be85948faadbd8b8a15dfaed45c4da7"
+        "sha": "3699b36878fb9d50c50e7638ed1e46fd44ebcb41"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "4f4b1b9b8d8b52f1e9e4a76165896debce5ab7f1"
+        "sha": "c86c7a60985644eab557949363a38301d40d78d2"
       }
     }
   ]

README.md

@@ -38,7 +38,7 @@ If you are using Maven without BOM, add this to your dependencies:
 <dependency>
   <groupId>com.google.cloud</groupId>
   <artifactId>google-cloud-datastore</artifactId>
-  <version>1.106.3</version>
+  <version>1.106.4</version>
 </dependency>
 
 ```