Remove trailing whitespace from license text

lib/spack/spack/cmd/list.py

lib/spack/spack/cmd/providers.py

lib/spack/spack/cmd/purge.py

lib/spack/spack/cmd/python.py

lib/spack/spack/cmd/spec.py

lib/spack/spack/cmd/stage.py

lib/spack/spack/cmd/test.py

lib/spack/spack/cmd/uninstall.py

lib/spack/spack/cmd/versions.py

lib/spack/spack/colify.py

lib/spack/spack/color.py

lib/spack/spack/compilation.py

lib/spack/spack/compilers/__init__.py

lib/spack/spack/compilers/gcc.py

lib/spack/spack/compilers/intel.py

lib/spack/spack/concretize.py

lib/spack/spack/directory_layout.py

lib/spack/spack/error.py

lib/spack/spack/globals.py

lib/spack/spack/multimethod.py