introduce variable for aas4j version

For easier aas4j version upgrading, aas4j-version variable introduced.

pom.xml

@@ -45,6 +45,7 @@
 		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
 		<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
 		<revision>2.0.0-SNAPSHOT</revision>
+		<aas4j-version>1.0.0-milestone-03.1</aas4j-version>
 	</properties>
 	<build>
 		<plugins>
@@ -133,7 +134,7 @@
 			<dependency>
 				<groupId>org.eclipse.digitaltwin.aas4j</groupId>
 				<artifactId>model</artifactId>
-				<version>1.0.0-milestone-03</version>
+				<version>${aas4j-version}</version>
 				<exclusions>
 					<exclusion>
 						<groupId>org.slf4j</groupId>
@@ -144,7 +145,7 @@
 			<dependency>
 				<groupId>org.eclipse.digitaltwin.aas4j</groupId>
 				<artifactId>dataformat-json</artifactId>
-				<version>1.0.0-milestone-03</version>
+				<version>${aas4j-version}</version>
 				<exclusions>
 					<exclusion>
 						<groupId>org.slf4j</groupId>
@@ -155,7 +156,7 @@
 			<dependency>
 				<groupId>org.eclipse.digitaltwin.aas4j</groupId>
 				<artifactId>dataformat-xml</artifactId>
-				<version>1.0.0-milestone-03</version>
+				<version>${aas4j-version}</version>
 				<exclusions>
 					<exclusion>
 						<groupId>org.slf4j</groupId>
@@ -166,7 +167,7 @@
 			<dependency>
 				<groupId>org.eclipse.digitaltwin.aas4j</groupId>
 				<artifactId>dataformat-aasx</artifactId>
-				<version>1.0.0-milestone-03</version>
+				<version>${aas4j-version}</version>
 				<exclusions>
 					<exclusion>
 						<groupId>org.slf4j</groupId>