poke: code modernization and cleanup

Change-Id: Ia0d5f0b1bc495636f8fac127bec735cc35af66a7
diff --git a/tools/peek/ndnpeek/main.cpp b/tools/peek/ndnpeek/main.cpp
index 1586387..f763b96 100644
--- a/tools/peek/ndnpeek/main.cpp
+++ b/tools/peek/ndnpeek/main.cpp
@@ -39,7 +39,7 @@
 static void
 usage(std::ostream& os, const std::string& program, const po::options_description& options)
 {
-  os << "Usage: " << program << " [options] ndn:/name\n"
+  os << "Usage: " << program << " [options] /name\n"
      << "\n"
      << "Fetch one data item matching the specified name and write it to the standard output.\n"
      << options;