Update nexus-staging-maven-plugin to 1.6.13

This will fix the issue `An API incompatibility was encountered while executing org.sonatype.plugins:nexus-staging-maven-plugin:1.6.7:deploy`

pom.xml

@@ -142,7 +142,7 @@
  <plugin>
  <groupId>org.sonatype.plugins</groupId>
  <artifactId>nexus-staging-maven-plugin</artifactId>
- <version>1.6.7</version>
+ <version>1.6.13</version>
  <extensions>true</extensions>
  <configuration>
  <serverId>ossrh</serverId>