Make the Maven quickstart artifact version default to aem_version_short

tasks/download/nexus.yml

@@ -13,5 +13,5 @@
     extension: jar
     username: "{{ nexus_username }}"
     password: "{{ nexus_password }}"
-    version: "{{ item.version }}"
+    version: "{{ item.version | default(aem_version_short) }}"
   with_items: "{{ aem_mvn_coordinates }}"