message: Updates fmt usage in multimat
diff: #include "axom/core.hpp"
  #include "axom/slam.hpp"
  -#include "fmt/fmt.hpp"
  +#include "axom/fmt.hpp"
  #include <iostream>
  #include <fstream>
  @@ -38,7 +38,7 @@ struct Value_Checker
  if(values.size() != vec.size())
  {
  SLIC_ERROR(
  - fmt::format("Sizes of arrays are different. 'values' has {} "
  + axom::fmt::format("Sizes of arrays are different. 'values' has {} "
  "elements; 'vec' has {} elements",
  values.size(),
  vec.size()));
  