Update quay.io/coreos/clair Docker tag to v4.2.0

This MR contains the following updates:

Package	Type	Update	Change
quay.io/coreos/clair	ironbank-docker	minor	v4.1.2 -> v4.2.0
quay.io/coreos/clair		minor	v4.1.2 -> v4.2.0
quay.io/coreos/clair	stage	minor	v4.1.2 -> v4.2.0

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