Bump the minimum required version of CMake to 3.12

[jmcarcell]

BEGINRELEASENOTES

• Bump the minimum required version of CMake to 3.12

ENDRELEASENOTES

3.12 instead of 3.10 so that CMP0074 is set to NEW by default. I wanted to remove the following warning:

  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.