FIX: use correct string for cache key

src/main/java/org/caosdb/server/query/Query.java

@@ -1007,7 +1007,7 @@ public class Query implements QueryInterface, ToElementable, TransactionInterfac
   String getCacheKey() {
     final StringBuilder sb = new StringBuilder();
     if (this.user != null) {
-      sb.append(this.user.toString());
+      sb.append(this.user.getPrincipal().toString());
     }
     if (this.versioned) {
       sb.append("versioned");