chore: regenerate README (googleapis#592)

This PR was generated using Autosynth. 🌈


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

```
2021-06-16 19:28:08,253 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-storage-nio/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-06-16 19:28:09,567 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/fd4bb4cb-2b5d-4c4c-8d50-86aaf4767fe6/targets

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

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-storage-nio.git",
-        "sha": "812a030928a1d8f5d02326120c94d739338ddff2"
+        "sha": "afba5a9f0e0ae218120b04d3dd976637f2843e81"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "2430f8d90ed8a508e8422a3a7191e656d5a6bf53"
+        "sha": "8f76a885deaaf2fe234daeba4a8cc4d1b3de8086"
       }
     }
   ]

README.md

@@ -42,7 +42,7 @@ If you are using Maven without BOM, add this to your dependencies:
 <dependency>
   <groupId>com.google.cloud</groupId>
   <artifactId>google-cloud-nio</artifactId>
-  <version>0.123.1</version>
+  <version>0.123.2</version>
 </dependency>
 
 ```
@@ -55,12 +55,12 @@ compile 'com.google.cloud:google-cloud-nio'
 ```
 If you are using Gradle without BOM, add this to your dependencies
 ```Groovy
-compile 'com.google.cloud:google-cloud-nio:0.123.1'
+compile 'com.google.cloud:google-cloud-nio:0.123.2'
 ```
 
 If you are using SBT, add this to your dependencies
 ```Scala
-libraryDependencies += "com.google.cloud" % "google-cloud-nio" % "0.123.1"
+libraryDependencies += "com.google.cloud" % "google-cloud-nio" % "0.123.2"
 ```
 
 ## Authentication