upgrade plugins

maven-gpg-plugin -> 3.0.1
nexus-staging-maven-plugin -> 1.6.13

pom.xml

@@ -240,7 +240,7 @@
 					<plugin>
 						<groupId>org.apache.maven.plugins</groupId>
 						<artifactId>maven-gpg-plugin</artifactId>
-						<version>1.6</version>
+						<version>3.0.1</version>
 						<executions>
 							<execution>
 								<id>sign-artifacts</id>
@@ -294,20 +294,11 @@
 		</profile>
 	</profiles>
 	<build>
-		<pluginManagement>
-			<plugins>
-				<plugin>
-					<groupId>org.apache.maven.plugins</groupId>
-					<artifactId>maven-release-plugin</artifactId>
-					<version>2.5.3</version>
-				</plugin>
-			</plugins>
-		</pluginManagement>
 		<plugins>
 			<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>ossrh</serverId>