chore: regenerate README (#285)

This PR was generated using Autosynth. 🌈


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

```
2020-12-14 20:04:34,992 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-billing/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2020-12-14 20:04:35,918 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/e77f5e5a-a1f6-4f55-8328-b23fc753dac7/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": "1b63d7faa09aa923414efeffffece466694c9c6d"
+        "sha": "6b02d8e60562d7644b42ea4202c51a701a422965"
       }
     },
     {

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>1.1.8</version>
+  <version>1.1.9</version>
 </dependency>
 
 ```