build: Fix compilation with boost 1.59

Change-Id: I1316c6d1151f8400f4370b68d098e61a25fd04c6
Refs: #3227
diff --git a/tests/unit-tests/security/identity-fixture.cpp b/tests/unit-tests/security/identity-fixture.cpp
index 36f9c0b..a89eb8d 100644
--- a/tests/unit-tests/security/identity-fixture.cpp
+++ b/tests/unit-tests/security/identity-fixture.cpp
@@ -113,6 +113,9 @@
 };
 
 BOOST_GLOBAL_FIXTURE(IdentityFixture)
+#if BOOST_VERSION >= 105900
+;
+#endif // BOOST_VERSION >= 105900
 
 } // namespace security
 } // namespace ndn