Update meshio to 5.3.4

[pyup-bot]

This PR updates meshio from 4.3.11 to 5.3.4.

Changelog

5.1.0

- CellBlocks are no longer tuples, but classes. You can no longer iterate over them like
python
for cell_type, cell_data in cells:
   pass

Instead, use
python
for cell_block in cells:
   cell_block.type
   cell_block.data

5.0.0

- meshio now only provides one command-line tool, `meshio`, with subcommands like
`info`, `convert`, etc. This replaces the former `meshio-info`, `meshio-convert` etc.

4.4.0

- Polygons are now stored as `"polygon"` cell blocks, not `"polygonN"` (where `N` is the
number of nodes per polygon). One can simply retrieve the number of points via
`cellblock.data.shape[1]`.

Links

• PyPI: https://pypi.org/project/meshio
• Changelog: https://pyup.io/changelogs/meshio/
• Repo: https://github.com/nschloe/meshio

[pyup-bot]

Closing this in favor of #260