Upgrade to nexus-staging-maven-plugin 1.6.13.

Resolves #1297.

Author: gregturn

pom.xml

@@ -506,7 +506,7 @@
                         <plugin>
                             <groupId>org.sonatype.plugins</groupId>
                             <artifactId>nexus-staging-maven-plugin</artifactId>
-                            <version>1.6.8</version>
+                            <version>1.6.13</version>
                             <extensions>true</extensions>
                             <configuration>
                                 <serverId>sonatype</serverId>