fixed typo in graphdb_test failure message

Signed-off-by: Riley Guerin <rileytg.dev@gmail.com>

pkg/graphdb/graphdb_test.go

@@ -121,7 +121,7 @@ func TestParents(t *testing.T) {
 		}
 
 		if len(parents) != 1 {
-			t.Fatalf("Expected 2 entries for %s got %d", key, len(parents))
+			t.Fatalf("Expected 1 entry for %s got %d", key, len(parents))
 		}
 
 		if parents[0] != p {