chore: regenerate README (#1287)

This PR was generated using Autosynth. 🌈


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

```
2021-05-10 17:51:57,320 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-bigquery/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-05-10 17:51:58,637 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/cc61bd79-d786-4237-a791-d0e60a08c582/targets

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

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-bigquery.git",
-        "sha": "70ca2652fd5843d9c8107d2317fa699bd0c9fca3"
+        "sha": "0fdaab4c8c65cf62e222f3c1bdac5e24049c37ad"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "06a8cd0ff7e81b05e6c503eab510ec622384caa7"
+        "sha": "6726988c677bb78385868bfc48dbfa2fe981d44a"
       }
     }
   ]

README.md

@@ -19,7 +19,7 @@ See https://github.com/GoogleCloudPlatform/cloud-opensource-java/wiki/The-Google
     <dependency>
       <groupId>com.google.cloud</groupId>
       <artifactId>libraries-bom</artifactId>
-      <version>20.2.0</version>
+      <version>20.3.0</version>
       <type>pom</type>
       <scope>import</scope>
     </dependency>
@@ -47,7 +47,7 @@ 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:20.2.0')
+implementation platform('com.google.cloud:libraries-bom:20.3.0')
 
 compile 'com.google.cloud:google-cloud-bigquery'
 ```