Fixed C++ level required

Author: JohanMabille

docs/source/index.rst

@@ -22,7 +22,7 @@ operators as for single values. It also provides accelerated implementation of c
 You can find out more about this implementation of C++ wrappers for SIMD intrinsics at the `The C++ Scientist`_. The mathematical functions are a
 lightweight implementation of the algorithms also used in `boost.SIMD`_.
 
-`xsimd` requires a C++14 compliant compiler. The following C++ compilers are supported:
+`xsimd` requires a C++11 compliant compiler. The following C++ compilers are supported:
 
 +-------------------------+-------------------------------+
 | Compiler                | Version                       |