chore: regenerate README (#522)

This PR was generated using Autosynth. 🌈


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

```
2021-08-27 15:05:59,607 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-datastore/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-08-27 15:06:00,634 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/1c2f57ff-17e8-439e-bdf8-73b2998a1e26/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": "e9db3f956dac1c56a376d5a57872a27181586994"
+        "sha": "a6a5b33f51dcd632d187c1b790d59cb6454d1efd"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "8032ab5a32471d85ece8fc261df16cc40fbfa4fb"
+        "sha": "31728d872f50e439ded2f67fa8d67955b26a4e35"
       }
     }
   ]

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>21.0.0</version>
+      <version>22.0.0</version>
       <type>pom</type>
       <scope>import</scope>
     </dependency>
@@ -49,7 +49,7 @@ 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:21.0.0')
+implementation platform('com.google.cloud:libraries-bom:22.0.0')
 
 compile 'com.google.cloud:google-cloud-datastore'
 ```