message: Improves recipe to find all files with Axom's copyright
  Using 'git grep' instead of 'find' only modifies files that are checked into the Axom repo.
diff: #!/usr/bin/env bash
  -# Copyright (c) 2017-2019, Lawrence Livermore National Security, LLC and
  +# Copyright (c) 2017-2020, Lawrence Livermore National Security, LLC and
  # other Axom Project Developers. See the top-level COPYRIGHT file for details.
  #
  # SPDX-License-Identifier: (BSD-3-Clause)
  #=============================================================================
  # First find all the files we want to modify
  #=============================================================================
  -find . -type f ! -name \*.git\* ! -name \*update_copyright\* -exec grep -l "other Axom Project Developers. See the top-level COPYRIGHT file for details." {} \; > files2change
  +git grep -l "other Axom Project Developers. See the top-level COPYRIGHT file for details." | grep -v update_copyright > files2change
  #=============================================================================
  # Replace the old copyright dates with new dates
  