chore: regenerate README (#408)

This PR was generated using Autosynth. 🌈


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

```
2021-05-19 21:09:35,141 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-servicedirectory/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-05-19 21:09:36,387 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/6dce9451-05f4-43a9-89bf-b221752c0116/targets

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

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-servicedirectory.git",
-        "sha": "49e41d67b2d1a946ebb06cbed8545b04377ac3ed"
+        "sha": "b603ec3453cb0a843a9bd617d1cda0597d2ff7fc"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "4f4b1b9b8d8b52f1e9e4a76165896debce5ab7f1"
+        "sha": "bf148334fb9ee928d4c302d2aa32eb61252808d1"
       }
     }
   ]

README.md

@@ -51,12 +51,12 @@ compile 'com.google.cloud:google-cloud-servicedirectory'
 ```
 If you are using Gradle without BOM, add this to your dependencies
 ```Groovy
-compile 'com.google.cloud:google-cloud-servicedirectory:1.2.3'
+compile 'com.google.cloud:google-cloud-servicedirectory:1.2.4'
 ```
 
 If you are using SBT, add this to your dependencies
 ```Scala
-libraryDependencies += "com.google.cloud" % "google-cloud-servicedirectory" % "1.2.3"
+libraryDependencies += "com.google.cloud" % "google-cloud-servicedirectory" % "1.2.4"
 ```
 
 ## Authentication