Bump requirement to a C++14 compiler

Author: mat007

README.md

@@ -8,4 +8,4 @@ Distributed under the [Boost Software License, Version 1.0](http://boost.org/LIC
 [![Build status](https://ci.appveyor.com/api/projects/status/459hvqkb5rts4hw7?svg=true)](https://ci.appveyor.com/project/mat007/turtle)
 [![Coverage Status](https://coveralls.io/repos/mat007/turtle/badge.png)](https://coveralls.io/r/mat007/turtle)
 
-Boost and a C++11 compatible compiler is required.
+Boost and a C++14 compatible compiler is required.