[C++] convert to c++14 for compilation.

Author: aschw

CMakeLists.txt

@@ -47,7 +47,7 @@ if (NOT CMAKE_BUILD_TYPE)
 endif (NOT CMAKE_BUILD_TYPE)
 
 if (NOT DEFINED CMAKE_CXX_STANDARD)
-    set(CMAKE_CXX_STANDARD 11)
+    set(CMAKE_CXX_STANDARD 14)
 endif ()
 
 if (NOT DEFINED CMAKE_CXX_EXTENSIONS)