demos: bump cmake version required to 3.15

This fixes problems finding the threads library.  There may
still be problems building these with TLS libraries added,
as those dependencies may not be satisfied if the library lacks
a cmake configuration file.

demo/async/CMakeLists.txt

@@ -1,13 +1,13 @@
 #
+# Copyright 2024 Staysail Systems, Inc. <[email protected]>
 # Copyright 2018 Capitar IT Group BV <[email protected]>
-# Copyright 2018 Staysail Systems, Inc. <[email protected]>
 #
 # This software is supplied under the terms of the MIT License, a
 # copy of which should be located in the distribution where this
 # file was obtained (LICENSE.txt).  A copy of the license may also be
 # found online at https://opensource.org/licenses/MIT.
 
-cmake_minimum_required (VERSION 2.8.12)
+cmake_minimum_required (VERSION 3.15)
 
 project(nng-asyncdemo)
 

demo/http_client/CMakeLists.txt

@@ -1,13 +1,13 @@
 #
 # Copyright 2018 Capitar IT Group BV <[email protected]>
-# Copyright 2018 Staysail Systems, Inc. <[email protected]>
+# Copyright 2024 Staysail Systems, Inc. <[email protected]>
 #
 # This software is supplied under the terms of the MIT License, a
 # copy of which should be located in the distribution where this
 # file was obtained (LICENSE.txt).  A copy of the license may also be
 # found online at https://opensource.org/licenses/MIT.
 
-cmake_minimum_required (VERSION 2.8.12)
+cmake_minimum_required (VERSION 3.15)
 
 project(http_client)
 

demo/pubsub_forwarder/CMakeLists.txt

@@ -3,7 +3,7 @@
 # file was obtained (LICENSE.txt).  A copy of the license may also be
 # found online at https://opensource.org/licenses/MIT.
 
-cmake_minimum_required(VERSION 3.10)
+cmake_minimum_required(VERSION 3.15)
 project(pubsub_forwarder C)
 
 # Find the nng library

demo/raw/CMakeLists.txt

@@ -1,13 +1,13 @@
 #
+# Copyright 2024 Staysail Systems, Inc. <[email protected]>
 # Copyright 2018 Capitar IT Group BV <[email protected]>
-# Copyright 2018 Staysail Systems, Inc. <[email protected]>
 #
 # This software is supplied under the terms of the MIT License, a
 # copy of which should be located in the distribution where this
 # file was obtained (LICENSE.txt).  A copy of the license may also be
 # found online at https://opensource.org/licenses/MIT.
 
-cmake_minimum_required (VERSION 2.8.12)
+cmake_minimum_required (VERSION 3.15)
 
 project(raw)
 

demo/reqrep/CMakeLists.txt

@@ -1,13 +1,13 @@
 #
+# Copyright 2024 Staysail Systems, Inc. <[email protected]>
 # Copyright 2018 Capitar IT Group BV <[email protected]>
-# Copyright 2018 Staysail Systems, Inc. <[email protected]>
 #
 # This software is supplied under the terms of the MIT License, a
 # copy of which should be located in the distribution where this
 # file was obtained (LICENSE.txt).  A copy of the license may also be
 # found online at https://opensource.org/licenses/MIT.
 
-cmake_minimum_required (VERSION 2.8.12)
+cmake_minimum_required (VERSION 3.15)
 
 project(reqrep)
 

demo/rest/CMakeLists.txt

@@ -1,13 +1,13 @@
 #
+# Copyright 2024 Staysail Systems, Inc. <[email protected]>
 # Copyright 2018 Capitar IT Group BV <[email protected]>
-# Copyright 2018 Staysail Systems, Inc. <[email protected]>
 #
 # This software is supplied under the terms of the MIT License, a
 # copy of which should be located in the distribution where this
 # file was obtained (LICENSE.txt).  A copy of the license may also be
 # found online at https://opensource.org/licenses/MIT.
 
-cmake_minimum_required (VERSION 2.8.12)
+cmake_minimum_required (VERSION 3.15)
 
 project(rest)
 

demo/stream/CMakeLists.txt

@@ -6,7 +6,7 @@
 # file was obtained (LICENSE.txt).  A copy of the license may also be
 # found online at https://opensource.org/licenses/MIT.
 
-cmake_minimum_required (VERSION 2.8.7)
+cmake_minimum_required (VERSION 3.15)
 
 project(stream)