Revert the removal of buildah dependency

We currently need it to drag in recent versions of other dependencies,
per https://github.com/containers/skopeo/issues/796 .

I'll work to update the relevant dependencies in c/image, but that will
only propagate to skopeo in the next c/image release; in the meantime,
this at least undoes the downgrades.

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

vendor/github.com/docker/distribution/registry/client/auth/challenge/authchallenge.go

@@ -45,13 +45,13 @@ type Manager interface {
 // to a backend.
 func NewSimpleManager() Manager {
 	return &simpleManager{
-		Challanges: make(map[string][]Challenge),
+		Challenges: make(map[string][]Challenge),
 	}
 }
 
 type simpleManager struct {
 	sync.RWMutex
-	Challanges map[string][]Challenge
+	Challenges map[string][]Challenge
 }
 
 func normalizeURL(endpoint *url.URL) {
@@ -64,7 +64,7 @@ func (m *simpleManager) GetChallenges(endpoint url.URL) ([]Challenge, error) {
 
 	m.RLock()
 	defer m.RUnlock()
-	challenges := m.Challanges[endpoint.String()]
+	challenges := m.Challenges[endpoint.String()]
 	return challenges, nil
 }
 
@@ -82,7 +82,7 @@ func (m *simpleManager) AddResponse(resp *http.Response) error {
 
 	m.Lock()
 	defer m.Unlock()
-	m.Challanges[urlCopy.String()] = challenges
+	m.Challenges[urlCopy.String()] = challenges
 	return nil
 }