build the test-jar (#158)

Added the test-jar goal to maven-jar-plugin.

# Checklist

The following aspects have been respected by the author of this pull
request, confirmed by both pull request assignee **and** reviewer:

* Adherence to coding conventions
  * [x] Pull Request Assignee
  * [x] Reviewer
* Adherence to javadoc conventions
  * [x] Pull Request Assignee
  * [x] Reviewer
* Changelog update (necessity checked and entry added or not added
respectively)
  * [x] Pull Request Assignee
  * [x] Reviewer
* README update (necessity checked and entry added or not added
respectively)
  * [x] Pull Request Assignee
  * [x] Reviewer
* config update (necessity checked and entry added or not added
respectively)
  * [x] Pull Request Assignee
  * [x] Reviewer
* SDCcc executable ran against a test device (if necessary)
  * [x] Pull Request Assignee
  * [x] Reviewer

pom.xml

@@ -85,6 +85,13 @@
                         </manifestSections>
                     </archive>
                 </configuration>
+                <executions>
+                    <execution>
+                        <goals>
+                            <goal>test-jar</goal>
+                        </goals>
+                    </execution>
+                </executions>
             </plugin>
 
             <plugin>