Update docs (C++11 -> C++17) (#2907)

Summary:
following #2899

This PR doesn't affect the software behavior

Pull Request resolved: #2907

Reviewed By: mdouze

Differential Revision: D46720499

Pulled By: algoriddle

fbshipit-source-id: 00b47baf526a94449e2b1c9ca5fcd4cf961f6f17

CONTRIBUTING.md

@@ -44,7 +44,7 @@ outlined on that page and do not file a public issue.
 
 * 4 or 2 spaces for indentation in C++ (no tabs)
 * 80 character line length (both for C++ and Python)
-* C++ language level: C++11
+* C++ language level: C++17
 
 ## License
 

INSTALL.md

@@ -73,7 +73,7 @@ found to run on other platforms as well, see
 [other platforms](https://github.com/facebookresearch/faiss/wiki/Related-projects#bindings-to-other-languages-and-porting-to-other-platforms).
 
 The basic requirements are:
-- a C++11 compiler (with support for OpenMP support version 2 or higher),
+- a C++17 compiler (with support for OpenMP support version 2 or higher),
 - a BLAS implementation (we strongly recommend using Intel MKL for best
 performance).