Upgrade maven-gpg-plugin 3.1.0 -> 3.2.0 (#1082)

See:
- https://issues.apache.org/jira/issues/?jql=project%20%3D%20MGPG%20AND%20fixVersion%20%3E%203.1.0%20AND%20fixVersion%20%3C%3D%203.2.0
- apache/maven-gpg-plugin@maven-gpg-plugin-3.1.0...maven-gpg-plugin-3.2.0

pom.xml

@@ -1068,7 +1068,7 @@
                 <plugin>
                     <groupId>org.apache.maven.plugins</groupId>
                     <artifactId>maven-gpg-plugin</artifactId>
-                    <version>3.1.0</version>
+                    <version>3.2.0</version>
                     <executions>
                         <execution>
                             <id>sign-artifacts</id>