Sync with underscore-java.

Author: javadev

pom-central.xml

@@ -100,7 +100,7 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
           <artifactId>maven-gpg-plugin</artifactId>
-          <version>1.4</version>
+          <version>1.6</version>
           <executions>
             <execution>
               <id>sign-artifacts</id>