Fix CMake warning while using CMake > 2.6.0

[dhruvkakadiya]

Include cmake_minimum_required check in examples/CMakeLists.txt to fix CMP0000 policy.

CMake Warning (dev) in CMakeLists.txt:
  No cmake_minimum_required command is present.  A line of code such as

    cmake_minimum_required(VERSION 3.14)

  should be added at the top of the file.  The version specified may be lower
  if you wish to support older CMake versions for this project.  For more
  information run "cmake --help-policy CMP0000".
This warning is for project developers.  Use -Wno-dev to suppress it.

[dhruvkakadiya]

Maybe that's not necessary unless we try to use examples/CMakeLists.txt individually and try to build examples from that directly and not root directory. But then there are other boost packages and lots of other things would be missing so doesn't look worthy to fix this.

[basiliscos]

It was intended, that you don't need to cmake for bredis project at all: just copy it to your project and it's done. It already assumes usage of boost::asio and it does not pulls in addtional dependencies.