Add missing dependency for testing ArchiveCommand with xz compression

Without this dependency the ArchiveTest.testTxzExtension() fails with a
ClassNotFoundException if it is started from Eclipse.

Change-Id: Ief2fceaaffab7641ba63ace4577462fa3bbf1c13
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit.pgm.test/META-INF/MANIFEST.MF

@@ -23,3 +23,4 @@ Import-Package: org.eclipse.jgit.api;version="[3.1.0,3.2.0)",
  org.hamcrest.core;bundle-version="[1.1.0,2.0.0)",
  org.junit;version="[4.4.0,5.0.0)",
  org.kohsuke.args4j;version="[2.0.12,2.1.0)"
+Require-Bundle: org.tukaani.xz;bundle-version="[1.3.0,2.0.0)"