chore: regenerate README (#916)

This PR was generated using Autosynth. 🌈


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

```
2020-11-05 23:02:58,892 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-bigquery/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working directory clean
2020-11-05 23:02:59,875 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/ab5a6234-7f62-4655-ad05-b0a7f1d1ba6e/targets

- [ ] To automatically regenerate this PR, check this box.

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

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-bigquery.git",
-        "sha": "77be64fc0084608e56d3b87e3e397506e36f455a"
+        "sha": "47c749f3e3ee6458d1cba7bde1a2c670bf35b9f6"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "ba9918cd22874245b55734f57470c719b577e591"
+        "sha": "2c8aecedd55b0480fb4e123b6e07fa5b12953862"
       }
     }
   ]

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>14.4.1</version>
+      <version>15.0.0</version>
       <type>pom</type>
       <scope>import</scope>
     </dependency>