table: NameTree code style corrections

refs #3687

Change-Id: I25cfac1d8b11236c251c2ab717facb82b62dcb10
diff --git a/daemon/table/measurements-entry.hpp b/daemon/table/measurements-entry.hpp
index 8eb40ff..933baef 100644
--- a/daemon/table/measurements-entry.hpp
+++ b/daemon/table/measurements-entry.hpp
@@ -32,11 +32,11 @@
 
 namespace nfd {
 
-class NameTree;
-
 namespace name_tree {
+class NameTree;
 class Entry;
 } // namespace name_tree
+using name_tree::NameTree;
 
 namespace measurements {