[Capnproto] Fixed CMake Compatibility Error

On CI, A CMake deprecation error occurs since CMake version < 3.5 will
be removed in a future version of CMake.

On the dev branch of CapNProto, they fixed this issue by setting the
minimum CMake version to 3.16:
capnproto/capnproto@2354ae2

Replicated these changes locally. Hopefully the next time we upgrade
CapNProto this will be in the changes.

Author: AlexandreSinger

libs/EXTERNAL/capnproto/CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.4)
+cmake_minimum_required(VERSION 3.16)
 project("Cap'n Proto Root" CXX)
 include(CTest)
 

libs/EXTERNAL/capnproto/c++/CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.6)
+cmake_minimum_required(VERSION 3.16)
 project("Cap'n Proto" CXX)
 set(VERSION 1.0.2)
 

libs/EXTERNAL/capnproto/c++/samples/CMakeLists.txt

@@ -17,7 +17,7 @@
 #      cmake --build .
 
 project("Cap'n Proto Samples" CXX)
-cmake_minimum_required(VERSION 3.1)
+cmake_minimum_required(VERSION 3.16)
 
 find_package(CapnProto CONFIG REQUIRED)
 

libs/EXTERNAL/capnproto/doc/install.md

@@ -116,7 +116,7 @@ If you want to use Cap'n Proto in C++ with Visual Studio, do the following:
    Proto uses C++14 language features that did not work in previous versions of Visual Studio,
    and the updates include many bug fixes that Cap'n Proto requires.
 
-2. Install [CMake](http://www.cmake.org/) version 3.1 or later.
+2. Install [CMake](http://www.cmake.org/) version 3.16 or later.
 
 3. Use CMake to generate Visual Studio project files under `capnproto-c++-1.0.2` in the zip file.
    You can use the CMake UI for this or run this shell command: