chore: regenerate README (#532)

This PR was generated using Autosynth. 🌈


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

```
2021-09-08 15:41:46,846 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-datastore/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-09-08 15:41:47,965 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/cf5614d5-a6d6-4549-95dc-241ed722649c/targets

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

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-datastore.git",
-        "sha": "60a95791ffe048e87fa6b0ad2c43bbc1b1838a24"
+        "sha": "b1932d97b8263c2bcfdf31179bb5705988d8d516"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "9a238a0623879c3de129a376c6085d4a862f6eb9"
+        "sha": "17ee6e5c08f2eb47029beee4776ce990e56b3925"
       }
     }
   ]

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>22.0.0</version>
+      <version>23.0.0</version>
       <type>pom</type>
       <scope>import</scope>
     </dependency>
@@ -41,28 +41,28 @@ If you are using Maven without BOM, add this to your dependencies:
 <dependency>
   <groupId>com.google.cloud</groupId>
   <artifactId>google-cloud-datastore</artifactId>
-  <version>2.0.3</version>
+  <version>2.1.0</version>
 </dependency>
 
 ```
 
 If you are using Gradle 5.x or later, add this to your dependencies
 
 ```Groovy
-implementation platform('com.google.cloud:libraries-bom:22.0.0')
+implementation platform('com.google.cloud:libraries-bom:23.0.0')
 
 implementation 'com.google.cloud:google-cloud-datastore'
 ```
 If you are using Gradle without BOM, add this to your dependencies
 
 ```Groovy
-implementation 'com.google.cloud:google-cloud-datastore:2.0.3'
+implementation 'com.google.cloud:google-cloud-datastore:2.1.0'
 ```
 
 If you are using SBT, add this to your dependencies
 
 ```Scala
-libraryDependencies += "com.google.cloud" % "google-cloud-datastore" % "2.0.3"
+libraryDependencies += "com.google.cloud" % "google-cloud-datastore" % "2.1.0"
 ```
 
 ## Authentication