Pantable filters broken after Pandoc upgrade

[alerque]

I recently upgraded a number of production machines from Pandoc 2.9.2 to 2.10.1. I thought all was well, but it turns out all my jobs that include Pantable at any point are failing. Here is a MWE that illustrates my usage:

# head

```table
---
alignment: RL
width: [0.5, 0.5]
---
"foo","bar"
```

$ pandoc -F pantable -t markdwon+pipe_tables-multiline-tables-grid_tables-raw_html < input.md
Error running filter pantable:
Error in $.blocks[1].c: cannot unpack array of length 5 into a tuple of length 6

Although I should note that this can be simplified further: just outputting to -t html throws the same error, and the YAML table properties don't seem to matter.

[ickc]

Duplicate of #51.