build: more accurate Boost lib dependencies

See also named-data/ndn-cxx@5686c51b87b6a642aa2dc8d93e061caebbb226cc

Change-Id: I28cfc24c3d8f0dd16a7bdcec092090a09c024fdf
diff --git a/examples/wscript b/examples/wscript
index e6badbf..6cb8dd2 100644
--- a/examples/wscript
+++ b/examples/wscript
@@ -6,8 +6,8 @@
     # List all .cpp files (whole example in one .cpp)
     for ex in bld.path.ant_glob('*.cpp'):
         name = ex.change_ext('').path_from(bld.path.get_bld())
-        bld.program(name='example-%s' % name,
-                    target='nac-%s' % name,
+        bld.program(name=f'example-{name}',
+                    target=f'nac-{name}',
                     source=[ex],
                     use='libndn-nac',
                     install_path=None)
@@ -15,7 +15,7 @@
     # List all directories (example can have multiple .cpp in the directory)
     for subdir in bld.path.ant_glob('*', dir=True, src=False):
         name = subdir.path_from(bld.path)
-        bld.program(name='example-%s' % name,
+        bld.program(name=f'example-{name}',
                     target=name,
                     source=subdir.ant_glob('**/*.cpp'),
                     use='libndn-nac',