Use c++17 as abseil-cpp now compiled with c++17

diff --git a/cpp/CMakeLists.txt b/cpp/CMakeLists.txt
index 434c593..5ae919b 100644
--- a/cpp/CMakeLists.txt
+++ b/cpp/CMakeLists.txt
@@ -18,7 +18,7 @@ cmake_minimum_required (VERSION 3.11)
 
 # Pick the C++ standard to compile with.
 # Abseil currently supports C++11, C++14, and C++17.
-set(CMAKE_CXX_STANDARD 11 CACHE STRING "C++ standard used to compile this project")
+set(CMAKE_CXX_STANDARD 17 CACHE STRING "C++ standard used to compile this project")
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 
 project (libphonenumber)