build: more accurate dependencies on Boost libraries

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

Change-Id: I0ff9b60ae9a5e51f597d16221bbe1d97afc9704a
diff --git a/examples/wscript b/examples/wscript
index c737d81..3be8951 100644
--- a/examples/wscript
+++ b/examples/wscript
@@ -6,7 +6,7 @@
     # 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='psync-%s' % name,
+        bld.program(name=f'example-{name}',
+                    target=f'psync-{name}',
                     source=[ex],
-                    use='PSync')
\ No newline at end of file
+                    use='PSync')