build: Fix installation path of the shared library

Change-Id: Iaa9e0f00c05a3af9d10bb0058be058be444156ca
diff --git a/wscript b/wscript
index 8cb55dc..8c789fc 100644
--- a/wscript
+++ b/wscript
@@ -69,6 +69,7 @@
         use = 'NDN_CXX BOOST',
         includes = ['src'],
         export_includes=['src'],
+        install_path='${LIBDIR}'
     )
 
     bld.recurse('tools')