Update maven-gpg-plugin to latest version

Otherwise, gpg-signing with GPG 2.1+ fails with:

  gpg: signing failed: No such file or directory

See also:
https://myshittycode.com/2017/08/07/maven-gpg-plugin-prevent-signing-prompt-or-gpg-signing-failed-no-such-file-or-directory-error/

Author: ctrueden

pom.xml

@@ -238,7 +238,7 @@
 		<maven-deploy-plugin.version>2.8.2</maven-deploy-plugin.version>
 		<maven-enforcer-plugin.version>3.0.0-M3</maven-enforcer-plugin.version>
 		<maven-failsafe-plugin.version>2.22.2</maven-failsafe-plugin.version>
-		<maven-gpg-plugin.version>1.6</maven-gpg-plugin.version>
+		<maven-gpg-plugin.version>3.0.1</maven-gpg-plugin.version>
 		<maven-install-plugin.version>2.5.2</maven-install-plugin.version>
 		<maven-invoker-plugin.version>3.2.1</maven-invoker-plugin.version>
 		<maven-jar-plugin.version>3.2.0</maven-jar-plugin.version>