chore: regenerate README (#656)

This PR was generated using Autosynth. 🌈


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

```
2021-08-19 17:21:08,985 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-storage-nio/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-08-19 17:21:09,993 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/8e6a83ef-59e4-4cb3-ac08-64cb62bcfb9e/targets

- [ ] To automatically regenerate this PR, check this box. (May take up to 24 hours.)

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

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-storage-nio.git",
-        "sha": "84d90a82eff6acf4ab21d3cac3d48a8ea73e5999"
+        "sha": "44d80d22a9470708f47d3e99452ca913e011f802"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "a01e1a0bf70754f51450958b966bd673945d1e6e"
+        "sha": "484b7ec7bdef3909589a83e3d763e7588cb8c37c"
       }
     }
   ]

README.md

@@ -45,7 +45,7 @@ If you are using Maven without BOM, add this to your dependencies:
 <dependency>
   <groupId>com.google.cloud</groupId>
   <artifactId>google-cloud-nio</artifactId>
-  <version>0.123.5</version>
+  <version>0.123.6</version>
 </dependency>
 
 ```