message: fix variable use
diff: @@ -521,7 +521,7 @@ class Axom(CachedCMakePackage, CudaPackage, ROCmPackage):
  def cmake_args(self):
  options = []
  - options.append("-DBLT_SOURCE_DIR:PATH={0}".format(spec["blt"].prefix))
  + options.append("-DBLT_SOURCE_DIR:PATH={0}".format(self.spec["blt"].prefix))
  if self.run_tests is False:
  options.append("-DENABLE_TESTS=OFF")
  