build: migrate to C++17

Change-Id: Ic9f09efd20b608bfcb713fd319834b2666cf6242
diff --git a/tests/io-key-chain-fixture.hpp b/tests/io-key-chain-fixture.hpp
index 199bd28..89ab07b 100644
--- a/tests/io-key-chain-fixture.hpp
+++ b/tests/io-key-chain-fixture.hpp
@@ -25,14 +25,12 @@
 #include "tests/key-chain-fixture.hpp"
 #include "tests/io-fixture.hpp"
 
-namespace nlsr {
-namespace test {
+namespace nlsr::test {
 
 class IoKeyChainFixture : public IoFixture, public KeyChainFixture
 {
 };
 
-} // namespace test
-} // namespace nlsr
+} // namespace nlsr::test
 
 #endif // NLSR_TESTS_IO_KEY_CHAIN_FIXTURE_HPP