[LyX/2.3.x] Cmake build: Remove some deprecation warnings

[Kornel Benko]

commit 4e59593514d4a65d54839b5ad7b1cc52c38802a4
Author: Kornel Benko <kornel at lyx.org>
Date:   Sat Oct 16 11:31:31 2021 +0200

    Cmake build: Remove some deprecation warnings
---
 3rdparty/hunspell/CMakeLists.txt |    2 +-
 3rdparty/mythes/CMakeLists.txt   |    2 +-
 3rdparty/zlib/CMakeLists.txt     |    2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/3rdparty/hunspell/CMakeLists.txt b/3rdparty/hunspell/CMakeLists.txt
index 7805b0e..dce94e4 100644
--- a/3rdparty/hunspell/CMakeLists.txt
+++ b/3rdparty/hunspell/CMakeLists.txt
@@ -1,5 +1,5 @@
 
-cmake_minimum_required(VERSION 2.8)
+cmake_minimum_required(VERSION 3.1)
 
 project(hunspell)
 
diff --git a/3rdparty/mythes/CMakeLists.txt b/3rdparty/mythes/CMakeLists.txt
index c6d1178..5449599 100644
--- a/3rdparty/mythes/CMakeLists.txt
+++ b/3rdparty/mythes/CMakeLists.txt
@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 2.8)
+cmake_minimum_required(VERSION 3.1)
 
 set(VERSION "1.2.5")
 set(SRCDIR ${CMAKE_CURRENT_SOURCE_DIR}/${VERSION})
diff --git a/3rdparty/zlib/CMakeLists.txt b/3rdparty/zlib/CMakeLists.txt
index c29081f..f65e334 100644
--- a/3rdparty/zlib/CMakeLists.txt
+++ b/3rdparty/zlib/CMakeLists.txt
@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 2.4.4)
+cmake_minimum_required(VERSION 3.1)
 set(CMAKE_ALLOW_LOOSE_LOOP_CONSTRUCTS ON)
 
 project(zlib C)