upgrade minimum cmake version (#255)

This will silence the following warning:

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.

CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required (VERSION 3.0.0)
+cmake_minimum_required (VERSION 3.5)
 
 include (utils.cmake)