Update minimum cmake version to 3.5

[paulober]

CMake as deprecated backwards compatibility for cmake versions < 3.5:

CMake Deprecation Warning at CMakeLists.txt:1 (cmake_minimum_required):
  Compatibility with CMake < 3.5 will be removed from a future version of
  CMake.

  Update the VERSION argument <min> value or use a ...<max> suffix to tell
  CMake that the project does not need compatibility with older versions.

I'm not sure why you set it so low, so I only increased it to the minimum supported version.

[patrickbr]

Thanks!

I'm not sure why you set it so low

Historic reasons :D