Update to maven-gpg-plugin 1.6.

Author: andreasrosdal

pom.xml

@@ -173,7 +173,7 @@
             <plugin>
               <groupId>org.apache.maven.plugins</groupId>
               <artifactId>maven-gpg-plugin</artifactId>
-              <version>1.5</version>
+              <version>1.6</version>
               <executions>
                 <execution>
                   <id>sign-artifacts</id>