Defined a property to have a common maven-enforcer-plugin version

pom.xml

@@ -649,6 +649,7 @@
 				<plugin>
 					<groupId>org.apache.maven.plugins</groupId>
 					<artifactId>maven-enforcer-plugin</artifactId>
+					<version>${maven-enforcer-plugin-version}</version>
 					<executions>
 						<execution>
 							<id>enforce</id>
@@ -698,6 +699,7 @@
 									<pluginExecutionFilter>
 										<groupId>org.apache.maven.plugins</groupId>
 										<artifactId>maven-enforcer-plugin</artifactId>
+										<version>${maven-enforcer-plugin-version}</version>
 										<goals>
 											<goal>enforce</goal>
 										</goals>
@@ -779,7 +781,7 @@
 			<plugin>
 				<groupId>org.apache.maven.plugins</groupId>
 				<artifactId>maven-enforcer-plugin</artifactId>
-				<version>3.0.0-M3</version>
+				<version>${maven-enforcer-plugin-version}</version>
 				<executions>
 					<execution>
 						<id>enforce-files-exist</id>
@@ -889,6 +891,8 @@
 
 		<repository.externals.readonly>http://maven.research-infrastructures.eu/nexus/content/repositories/gcube-externals</repository.externals.readonly>
 
+		<maven-enforcer-plugin-version>3.0.0-M3</maven-enforcer-plugin-version>
+
 		<!-- following properties contains common information on gCube that are used for filtering resources like README, LICENSE, ... -->
 
 		<gcube.wikiRoot>https://wiki.gcube-system.org/gcube/index.php</gcube.wikiRoot>