[MINOR] maven-gpg-plugin update to version 3.0.1 (#1285)

gpg plugin does not sign the artifacts but simply provides .asc file.

- More about the plugin:
  https://maven.apache.org/plugins/maven-gpg-plugin/plugin-info.html

---
Commentary:

Signing artifacts with SHA-256 or higher using maven resolver, which is
part of maven core, but not with maven-gpg-plugin. If you are unable
to sign the artifacts then upgrade to latest maven version.

  ```sh
  mvn -P'distribution' deploy -Daether.checksums.algorithms=SHA-256
  ```

- The signing with SHA512 functionality has been added in 2016 by
  https://issues.apache.org/jira/browse/MPOM-118

pom.xml

@@ -689,7 +689,7 @@
 
 					<plugin>
 						<artifactId>maven-gpg-plugin</artifactId>
-						<version>1.6</version>
+						<version>3.0.1</version>
 						<executions>
 							<execution>
 								<phase>verify</phase>