build: do not declare javadoc plugin version (#1183)

Author: alicejli

README.md

@@ -23,20 +23,20 @@ If you are using Maven, add this to your pom.xml file:
 <dependency>
   <groupId>com.google.cloud</groupId>
   <artifactId>google-cloud-logging-logback</artifactId>
-  <version>0.130.22-alpha</version>
+  <version>0.130.23-alpha</version>
 </dependency>
 ```
 
 If you are using Gradle without BOM, add this to your dependencies:
 
 ```Groovy
-implementation 'com.google.cloud:google-cloud-logging-logback:0.130.22-alpha'
+implementation 'com.google.cloud:google-cloud-logging-logback:0.130.23-alpha'
 ```
 
 If you are using SBT, add this to your dependencies:
 
 ```Scala
-libraryDependencies += "com.google.cloud" % "google-cloud-logging-logback" % "0.130.22-alpha"
+libraryDependencies += "com.google.cloud" % "google-cloud-logging-logback" % "0.130.23-alpha"
 ```
 <!-- {x-version-update-end} -->
 
@@ -299,7 +299,7 @@ Java is a registered trademark of Oracle and/or its affiliates.
 [kokoro-badge-link-5]: http://storage.googleapis.com/cloud-devrel-public/java/badges/java-logging-logback/java11.html
 [stability-image]: https://img.shields.io/badge/stability-preview-yellow
 [maven-version-image]: https://img.shields.io/maven-central/v/com.google.cloud/google-cloud-logging-logback.svg
-[maven-version-link]: https://central.sonatype.com/artifact/com.google.cloud/google-cloud-logging-logback/0.130.22-alpha
+[maven-version-link]: https://central.sonatype.com/artifact/com.google.cloud/google-cloud-logging-logback/0.130.23-alpha
 [authentication]: https://github.com/googleapis/google-cloud-java#authentication
 [auth-scopes]: https://developers.google.com/identity/protocols/oauth2/scopes
 [predefined-iam-roles]: https://cloud.google.com/iam/docs/understanding-roles#predefined_roles

pom.xml

@@ -180,7 +180,6 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-javadoc-plugin</artifactId>
-        <version>3.6.0</version>
         <reportSets>
           <reportSet>
             <id>html</id>