.mailmap: add "Noam Postavsky"

Committed as "npostavs" in 94fddadd, but as "Noam Postavsky" in
fc6f4814, which would cause duplicates in the "AUTHORS.md" file.

Signed-off-by: Pieter Praet <pieter@praet.org>
AUTHORS.md: auto-generated using 'make authors'

Signed-off-by: Pieter Praet <pieter@praet.org>
Merge pull request #838 from praet/authors

update .mailmap and AUTHORS.md