chore: regenerate README (#1037)

This PR was generated using Autosynth. 🌈


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

```
2021-04-26 23:22:32,688 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-bigquerystorage/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-04-26 23:22:33,990 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/55381f3c-91b5-4ee3-a216-1bfcb7d992a3/targets

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

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-bigquerystorage.git",
-        "sha": "776c670267d2c9bbc730c41f8187ac853b8525d3"
+        "sha": "6b8c0bd0e3908f600b8c439c16d73896cdfa1bca"
       }
     },
     {

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-bigquerystorage</artifactId>
-  <version>1.20.0</version>
+  <version>1.20.1</version>
 </dependency>
 
 ```