style(commitlint): reorder header/body max line length fields

This change simply reorders the `body-max-line-length` and
`header-max-line-length` fields to be in the order that most people
mentally expect. This has no actual function impact.

Change-Id: Ice0db951e4049baaf4de9372255407adc4e3bf66
Signed-off-by: Chris Kay <chris.kay@arm.com>