Update user lists for IBM platform teams

[miladfarca]

The user list in these groups may need to be updated. Do the listed users still need to be included?

• https://github.com/orgs/nodejs/teams/platform-ppc
  • AshCripps
• https://github.com/orgs/nodejs/teams/platform-s390
  • Ash Cripps
• https://github.com/orgs/nodejs/teams/platform-aix
  • Michael Felt, Ash Cripps
• https://github.com/orgs/nodejs/teams/platform-ibmi
  • mgoffmn, Vasili Skurydzin

[miladfarca]

FYI @richardlau