[MIME4J-308] Update tarLongFileMode to use POSIX (#60)

diff --git a/assemble/pom.xml b/assemble/pom.xml
index c60411b..e5ca2ba 100644
--- a/assemble/pom.xml
+++ b/assemble/pom.xml
@@ -59,7 +59,7 @@
                 <version>3.1.1</version>
                 <configuration>
                     <descriptorSourceDirectory>${basedir}/src/assemble/</descriptorSourceDirectory>
-                    <tarLongFileMode>gnu</tarLongFileMode>
+                    <tarLongFileMode>posix</tarLongFileMode>
                 </configuration>
                 <executions>
                     <execution>