message: Updates RELEASE-NOTES for new template parameter in ImplicitGrid
  This was changed in
diff: @@ -38,6 +38,8 @@ The Axom project release numbers follow [Semantic Versioning](http://semver.org/
  - `axom::Array` now default-initializes its data by default. To leave data uninitialized, pass
  an `axom::ArrayOptions::Uninitialized` as the first constructor argument
  - `axom::ArrayView<const T>` can now be created from a `const Array<T>`
  +- Added new `ExecSpace` template parameter to `spin::ImplicitGrid`.
  + `ExecSpace` is now the second template parameter (out of three) and defaults to `axom::SEQ_EXEC`.
  ### Fixed
  - Fixed a bug relating to swap and assignment operations for multidimensional `axom::Array`s
  