chore: regenerate README (googleapis#1485)

This PR was generated using Autosynth. 🌈


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

```
2021-08-05 20:57:10,116 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-bigquery/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-08-05 20:57:11,580 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/b0c41e37-9ebf-4dc3-8c47-d274948c81f0/targets

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

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-bigquery.git",
-        "sha": "af599a865b988191bb45182063c5fd9403b50f4c"
+        "sha": "6caf046d7504b0c21c15993152e4ae38c15f5edf"
       }
     },
     {

README.md

@@ -43,7 +43,7 @@ If you are using Maven without BOM, add this to your dependencies:
 <dependency>
   <groupId>com.google.cloud</groupId>
   <artifactId>google-cloud-bigquery</artifactId>
-  <version>1.137.2</version>
+  <version>2.0.0</version>
 </dependency>
 
 ```