Replace out-of-date nomenclature (#1213)
Replace out-of-date nomenclature (#1213)

Motivation:
Package *feed* was renamed to *collection*. There are still occurrences
of "feed" in the proposal.

Modifications:
Replace "feed" with "collection".
apple/swift-evolution,abertelrud/swift-evolution,apple/swift-evolution,abertelrud/swift-evolution,natecook1000/swift-evolution,natecook1000/swift-evolution