fix wrong cast in Reference#equals

src/de/uni_passau/fim/seibt/gitwrapper/repo/Reference.java

@@ -135,8 +135,8 @@ public abstract class Reference {
             return false;
         }
 
-        Commit commit = (Commit) o;
-        return Objects.equals(id, commit.id) && Objects.equals(repo, commit.repo);
+        Reference ref = (Reference) o;
+        return Objects.equals(id, ref.id) && Objects.equals(repo, ref.repo);
     }
 
     @Override