build: more accurate dependencies on Boost libraries

See also named-data/ndn-cxx@5686c51b87

Change-Id: I0ff9b60ae9a5e51f597d16221bbe1d97afc9704a

examples/wscript

@@ -6,7 +6,7 @@ def build(bld):
     # 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')
+                    use='PSync')