[C++] [Pistache] update cpp flag for pistache

Created by: etherealjoy

PR checklist

• Read the contribution guidelines.
• If contributing template-only or documentation-only changes which will change sample output, build the project before.
• Run the shell script(s) under ./bin/ (or Windows batch scripts under.\bin\windows) to update Petstore samples related to your fix. This is important, as CI jobs will verify all generator outputs of your HEAD commit, and these must match the expectations made by your contribution. You only need to run ./bin/{LANG}-petstore.sh, ./bin/openapi3/{LANG}-petstore.sh if updating the code or mustache templates for a language ({LANG}) (e.g. php, ruby, python, etc).
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Fixes #4378 (closed)

@muttleyxd @MartinDelille @ravinikam @stkrwork

modules/openapi-generator/src/main/resources/cpp-pistache-server/cmake.mustache

@@ -2,7 +2,7 @@ cmake_minimum_required (VERSION 3.2)
 
 project(api-server)
 
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -pg -g3" )
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++14 -pg -g3" )
 
 {{#addExternalLibs}}
 include(ExternalProject)

samples/server/petstore/cpp-pistache/.openapi-generator/VERSION

-4.2.0-SNAPSHOT
\ No newline at end of file
+4.2.1-SNAPSHOT
\ No newline at end of file

samples/server/petstore/cpp-pistache/CMakeLists.txt

@@ -2,7 +2,7 @@ cmake_minimum_required (VERSION 3.2)
 
 project(api-server)
 
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -pg -g3" )
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++14 -pg -g3" )
 
 include(ExternalProject)