Coreboot*Pkg/Contributions.txt: Update example email address

Coreboot*Pkg/Contributions.txt: Update example email address

Use the example.com domain as recommended in RFC 2606.

This was changed for the other EDK II packages in r16724.

NOTE: This does not modify the wording of the "TianoCore Contribution
      Agreement 1.0" section

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Maurice Ma <maurice.ma@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@17169 6f19259b-4bc3-4df7-8a09-765794883524