update nexus-staging-maven-plugin

to use the same as in ditto main repo

Author: thjaeckle

java/pom.xml

@@ -501,7 +501,7 @@
                 <plugin>
                     <groupId>org.sonatype.plugins</groupId>
                     <artifactId>nexus-staging-maven-plugin</artifactId>
-                    <version>1.6.8</version>
+                    <version>1.6.12</version>
                 </plugin>
                 <plugin>
                     <groupId>org.apache.maven.plugins</groupId>