Fix package signing configuration

Since the update of the nexus-staging-maven-plugin, the artifacts need to be
explicityly signed _before_ they are uploaded to OSSRH. Without this fix, an
OSSRH release is not possible since the signature files are missing.

Author: atextor

pom.xml

@@ -616,7 +616,7 @@
             <executions>
                <execution>
                   <id>sign-artifacts</id>
-                  <phase>deploy</phase>
+                  <phase>verify</phase>
                   <goals>
                      <goal>sign</goal>
                   </goals>