Bump cmake version requirement to 3.19

[peter-d]

Currently we require cmake 3.15 in the cmake files:

map/sparta/CMakeLists.txt

Line 1 in 8d04103

cmake_minimum_required (VERSION 3.15)

But, per cmake version history, the HDF5::HDF5 target we use, only got introduced in cmake 3.19:
Kitware/CMake@a8e0a6b

Context: this is currently breaking CI against sparta master in pr 42 of the Olympia model which still uses 3.17: https://github.com/riscv-software-src/riscv-perf-model/blob/boost_fix/conda/environment.yml

[peter-d]

Closing - #416 fixed this.