Fix bug with decimal precision and scale

[asfimport]

The precision and scale parameters are reversed in the MapWriters template.

Reporter: Steven Phillips / @StevenMPhillips
Assignee: Steven Phillips / @StevenMPhillips

_{Note: This issue was originally created as ARROW-18. Please see the migration documentation for further details.}

[asfimport]

Julien Le Dem / @julienledem:
Resolved in: 243ed4e
PR: #5