Change vendor to ub-mannheim

Change vendor from `slub` to `ub-mannheim` so that composer can find the dev branches

Signed-off-by: Christos Sidiropoulos <[email protected]>

composer.json

@@ -1,5 +1,5 @@
 {
-  "name": "slub/dfgviewer",
+  "name": "ub-mannheim/dfgviewer",
   "type": "typo3-cms-extension",
   "description": "Remote resources navigator for digital libraries. Reads METS/MODS and METS/TEI via OAI-PMH.",
   "homepage": "https://github.com/slub/dfg-viewer",