eslint: Missing “key” prop for element in iterator (react/jsx-key)

You should put the key on the outer element:

const peopleCard = this.state.people.map(person => (
  <Col key={person.id} sm="4">
    <PeopleCard person={person} />
  </Col>
));

Please take a time to notice that the Col element have an unique key. Indeed, person.id is unique throughout the map loop.