[CMake] Switch to C++14

As include/hpp/util/serialization.hh use `std::enable_if_t`, which is
only available in C++ >= 14

CMakeLists.txt

@@ -27,7 +27,7 @@ SET(PROJECT_USE_CMAKE_EXPORT TRUE)
 
 COMPUTE_PROJECT_ARGS(PROJECT_ARGS LANGUAGES CXX C)
 PROJECT(${PROJECT_NAME} ${PROJECT_ARGS})
-CHECK_MINIMAL_CXX_STANDARD(11 REQUIRED)
+CHECK_MINIMAL_CXX_STANDARD(14 REQUIRED)
 
 # Search for Boost.
 ADD_PROJECT_DEPENDENCY(Boost REQUIRED COMPONENTS filesystem serialization)