maven java.lang.NoClassDefFoundError: nu/pattern/OpenCV error

I am using https://github.com/patternconsulting/opencv to include opencv 3.2.0 in my maven java project.

The issue that I am facing is that when i use mvn install to generate a jar file and then run the jar file java -jar app.jar i get the following error:

Exception in thread "main" java.lang.NoClassDefFoundError: nu/pattern/OpenCV
    at com.example.Application.<clinit>(Application.java:21)
Caused by: java.lang.ClassNotFoundException: nu.pattern.OpenCV
    at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357)

below is an extract of my pom.xml file

       <dependency>
            <groupId>org.openpnp</groupId>
            <artifactId>opencv</artifactId>
            <version>3.2.0-1</version>
        </dependency>
    </dependencies>
    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-jar-plugin</artifactId>
                <version>3.0.2</version>
                <configuration>
                    <archive>
                        <manifest>
                            <addClasspath>true</addClasspath>
                            <addDefaultImplementationEntries>true</addDefaultImplementationEntries>
                            <mainClass>com.example.Application</mainClass>
                        </manifest>
                    </archive>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

and below is an extract of my class that has the main method:

public class Application {

    static {
        OpenCV.loadShared();
    }


    public Application() throws Exception {
      // some code here
    }

    public static void main(String[] args) {
            new Application();
    }

any idea what might be causing this to happen and how to solve it?

Thanks