make cmake enforce C++14 standard

RalphSteinhagen · RalphSteinhagen · commit 60450a98010f · 2022-03-14T21:49:19.000+01:00
see ReactiveX#572 (comment)
diff --git a/projects/CMake/CMakeLists.txt b/projects/CMake/CMakeLists.txt
@@ -1,6 +1,7 @@
 cmake_minimum_required(VERSION 3.2 FATAL_ERROR)
 
 project(rxcpp VERSION 2.2.4 LANGUAGES C CXX)
+set(CMAKE_CXX_STANDARD 14)
 
 set_property(GLOBAL PROPERTY USE_FOLDERS ON)
 
