Serialize packages before giving it to Django (#39)

It should fix #38, thanks @askoretskiy

src/statici18n/management/commands/compilejsi18n.py

@@ -57,7 +57,7 @@ def _create_javascript_catalog(self, locale, domain, packages):
             response = render_javascript_catalog(catalog, plural)
         else:
             catalog = JavaScriptCatalog()
-            packages = None if packages == 'django.conf' else packages
+            packages = None if packages == 'django.conf' else packages.join('+')
             # we are passing None as the request, as the request object is currently not used by django
             response = catalog.get(self, None, domain=domain, packages=packages)
         return force_text(response.content)
@@ -75,7 +75,7 @@ def _create_json_catalog(self, locale, domain, packages):
             return force_text(json.dumps(data, ensure_ascii=False))
         else:
             catalog = JSONCatalog()
-            packages = None if packages == 'django.conf' else packages
+            packages = None if packages == 'django.conf' else packages.join('+')
             # we are passing None as the request, as the request object is currently not used by django
             response = catalog.get(self, None, domain=domain, packages=packages)
             return force_text(response.content)