Missing version of maven-jar-plugin

[Rillke]

That warning sounds pretty serve:

bash-4.4# cd /opt/datatools-server/ && mvn package -DskipTests
[INFO] Scanning for projects...
[WARNING] 
[WARNING] Some problems were encountered while building the effective model for com.conveyal:datatools-server:jar:3.0.0-SNAPSHOT
[WARNING] 'build.plugins.plugin.version' for org.apache.maven.plugins:maven-jar-plugin is missing. @ line 85, column 21
[WARNING] 
[WARNING] It is highly recommended to fix these problems because they threaten the stability of your build.
[WARNING] 
[WARNING] For this reason, future Maven versions might no longer support building such malformed projects.
[WARNING] 

pom.xml currently looks like this:

            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-jar-plugin</artifactId>
                <configuration>
                    <archive>
                        <manifest>
                            <mainClass>com.conveyal.datatools.manager.DataManager</mainClass>
                        </manifest>
                    </archive>
                </configuration>
            </plugin>