chore: regenerate README (#379)

This PR was generated using Autosynth. 🌈


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

```
2020-10-08 21:55:55,073 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-pubsub/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working directory clean
2020-10-08 21:55:56,028 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/e406cfbe-f881-47cf-8da9-62e058d1ab12/targets

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

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

@@ -0,0 +1,18 @@
+{
+  "sources": [
+    {
+      "git": {
+        "name": ".",
+        "remote": "https://github.com/googleapis/java-pubsub.git",
+        "sha": "234505066757de6a391afa747e260d48a9b83fff"
+      }
+    },
+    {
+      "git": {
+        "name": "synthtool",
+        "remote": "https://github.com/googleapis/synthtool.git",
+        "sha": "b6164c26a111f7f587099d31253abb96b5737bb2"
+      }
+    }
+  ]
+}

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>10.1.0</version>
+      <version>12.0.0</version>
       <type>pom</type>
       <scope>import</scope>
     </dependency>