chore: regenerate README (#466)

This PR was generated using Autosynth. 🌈


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

```
2021-06-30 20:44:40,693 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-datastore/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-06-30 20:44:41,971 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/783c155b-832b-4440-ba35-172fd435f71c/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-datastore.git",
-        "sha": "147a3e5a80b2597258c4b78ae54d4be5d45b4df1"
+        "sha": "3f32c42e8ba62d1599b49f095d5b66e97f602ef9"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "9763f20e4b7bb1091082462b2f7970e965d0d414"
+        "sha": "39652e3948f455fd0b77535a0145eeec561a3706"
       }
     }
   ]

README.md

@@ -17,7 +17,7 @@ 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>20.6.0</version>
+      <version>20.7.0</version>
       <type>pom</type>
       <scope>import</scope>
     </dependency>