[releng] Update eclipse-jarsigner-plugin to 1.3.1

Up from 1.1.7. See [1] for the reason.

[1] https://www.eclipse.org/lists/cbi-dev/msg02374.html

Change-Id: Ia7c1c9f443793ce476acd6ddfe521ea488a1a60b
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>

org.eclipse.jgit.packaging/pom.xml

@@ -294,7 +294,7 @@
         <plugin>
           <groupId>org.eclipse.cbi.maven.plugins</groupId>
           <artifactId>eclipse-jarsigner-plugin</artifactId>
-          <version>1.1.7</version>
+          <version>1.3.1</version>
         </plugin>
         <plugin>
           <groupId>org.codehaus.mojo</groupId>