build: explicitly require libndn-cxx >= 0.8.0

Change-Id: I677dcec4e76cb63ef78927ab0befa42df83314ba
diff --git a/wscript b/wscript
index e5740f4..ad201d1 100644
--- a/wscript
+++ b/wscript
@@ -1,11 +1,11 @@
 # -*- Mode: python; py-indent-offset: 4; indent-tabs-mode: nil; coding: utf-8; -*-
 
-VERSION = '0.1'
-APPNAME = 'ndn-traffic-generator'
-
 from waflib import Utils
 import os
 
+VERSION = '0.1'
+APPNAME = 'ndn-traffic-generator'
+
 def options(opt):
     opt.load(['compiler_cxx', 'gnu_dirs'])
     opt.load(['default-compiler-flags'],
@@ -15,8 +15,9 @@
     conf.load(['compiler_cxx', 'gnu_dirs',
                'default-compiler-flags'])
 
-    conf.check_cfg(package='libndn-cxx', args=['--cflags', '--libs'], uselib_store='NDN_CXX',
-                   pkg_config_path=os.environ.get('PKG_CONFIG_PATH', '%s/pkgconfig' % conf.env.LIBDIR))
+    pkg_config_path = os.environ.get('PKG_CONFIG_PATH', f'{conf.env.LIBDIR}/pkgconfig')
+    conf.check_cfg(package='libndn-cxx', args=['libndn-cxx >= 0.8.0', '--cflags', '--libs'],
+                   uselib_store='NDN_CXX', pkg_config_path=pkg_config_path)
 
     conf.check_compiler_flags()