chore: regenerate README (#299)

This PR was generated using Autosynth. 🌈


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

```
2021-01-07 22:21:41,513 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-billing/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-01-07 22:21:42,366 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/1f25b7b7-2bc7-48cb-986f-65c3ab83b961/targets

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

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

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-billing.git",
-        "sha": "93dc7487cde78f9cb88eaaae1a9fbc36dee7d52e"
+        "sha": "66cd85b187ddcf567056c50d48852ff64c962de0"
       }
     },
     {

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-billing</artifactId>
-  <version>1.1.9</version>
+  <version>1.1.11</version>
 </dependency>
 
 ```