Maven bucklet: Add dummy license parameter

Synchonize the interfaces for maven_jar bucklet used in Gerrit core.
For now just ignore license parameter.

This is needed to allow to co-exist in tree and standalone plugins.

Change-Id: Iaf44a066f209940b8967e29200acf56eab04e8bb
diff --git a/maven_jar.bucklet b/maven_jar.bucklet
index 84812b7..20ebbe7 100644
--- a/maven_jar.bucklet
+++ b/maven_jar.bucklet
@@ -51,6 +51,7 @@
 def maven_jar(
     name,
     id,
+    license = '',
     exclude = [],
     exclude_java_sources = False,
     unsign = False,