chore: regenerate README (#332)

This PR was generated using Autosynth. 🌈


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

```
2020-12-14 19:57:22,022 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-secretmanager/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2020-12-14 19:57:22,917 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/8857a942-9409-41e3-acc8-924a02080220/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-secretmanager.git",
-        "sha": "1a2edeb0f0ee96c5edc9ce25a2413cdb845d15ce"
+        "sha": "99cad0d6de5b4b7fafa6a6165d13a9312198a0df"
       }
     },
     {

README.md

@@ -39,7 +39,7 @@ If you are using Maven without BOM, add this to your dependencies:
 <dependency>
   <groupId>com.google.cloud</groupId>
   <artifactId>google-cloud-secretmanager</artifactId>
-  <version>1.2.5</version>
+  <version>1.2.6</version>
 </dependency>
 
 ```