Use Boost.Operators in more places

Change-Id: I7024c3e7d4c30c99ec7a895d484f227cb60fb356
diff --git a/tests/unit/version.t.cpp b/tests/unit/version.t.cpp
index 527bc95..4b551a9 100644
--- a/tests/unit/version.t.cpp
+++ b/tests/unit/version.t.cpp
@@ -37,9 +37,9 @@
                                 NDN_CXX_VERSION_MINOR * 1000 +
                                 NDN_CXX_VERSION_PATCH);
 
-  static_assert(NDN_CXX_VERSION_MAJOR < 1000, "");
-  static_assert(NDN_CXX_VERSION_MINOR < 1000, "");
-  static_assert(NDN_CXX_VERSION_PATCH < 1000, "");
+  static_assert(NDN_CXX_VERSION_MAJOR < 1000);
+  static_assert(NDN_CXX_VERSION_MINOR < 1000);
+  static_assert(NDN_CXX_VERSION_PATCH < 1000);
 }
 
 BOOST_AUTO_TEST_CASE(VersionString)