chore: regenerate README (#526)

This PR was generated using Autosynth. 🌈


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

```
2021-06-10 15:13:23,278 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-kms/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-06-10 15:13:24,472 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/34b8a6ff-f1da-4210-ae1c-f5711b2f4c09/targets

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

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-kms.git",
-        "sha": "6872203a0fa0539ac786ea73645f4b06fd925558"
+        "sha": "d6bfb59b81a6b78857a93dec02df789328470a2c"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "2430f8d90ed8a508e8422a3a7191e656d5a6bf53"
+        "sha": "5cae043787729a908ed0cab28ca27baf9acee3c4"
       }
     }
   ]

README.md

@@ -52,12 +52,12 @@ compile 'com.google.cloud:google-cloud-kms'
 ```
 If you are using Gradle without BOM, add this to your dependencies
 ```Groovy
-compile 'com.google.cloud:google-cloud-kms:1.42.2'
+compile 'com.google.cloud:google-cloud-kms:1.42.3'
 ```
 
 If you are using SBT, add this to your dependencies
 ```Scala
-libraryDependencies += "com.google.cloud" % "google-cloud-kms" % "1.42.2"
+libraryDependencies += "com.google.cloud" % "google-cloud-kms" % "1.42.3"
 ```
 
 ## Authentication