build: align minimum build dependencies with ndn-cxx

 * gcc 7.4
 * clang 6.0
 * Xcode 10.0 (11.3 or later recommended)

Change-Id: I365e7b1e2c9b081e512f511bf5beee2487cfc361
diff --git a/wscript b/wscript
index 89287e8..270ac19 100644
--- a/wscript
+++ b/wscript
@@ -41,8 +41,9 @@
 
     conf.find_program('dot', var='DOT', mandatory=False)
 
-    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)
 
     boost_libs = ['system', 'iostreams']
     if conf.env.WITH_TESTS: