build: use base version in pkgconfig file

Change-Id: Ie63edcffa61caafca3d64e77753e45fee8ce55da
diff --git a/wscript b/wscript
index f9cee88..69ccebd 100644
--- a/wscript
+++ b/wscript
@@ -117,7 +117,7 @@
         source='libndn-nac.pc.in',
         target='libndn-nac.pc',
         install_path='${LIBDIR}/pkgconfig',
-        VERSION=VERSION)
+        VERSION=VERSION_BASE)
 
 def docs(bld):
     from waflib import Options