Bump cmake required version to 3.10

[rlalik]

Simple change in CMakeLists.txt due to this deprecation warning:

CMake Deprecation Warning at CMakeLists.txt:1 (cmake_minimum_required):
  Compatibility with CMake < 3.10 will be removed from a future version of
  CMake.

  Update the VERSION argument <min> value.  Or, use the <min>...<max> syntax
  to tell CMake that the project requires at least <min> but has been updated
  to work with policies introduced by <max> or earlier.

[lemire]

Thanks. It seems we bumped it to 3.10 earlier.

[rlalik]

Well, my PR was waiting 4 months so ;) But I'm glad it was done. Cheers!

[lemire]

@rlalik Squarely my fault, obviously.