Rename CommittedAt to CreatedAt in content interface

Use "created at" terminology to be consistent with the rest
of the containerd interfaces.

Signed-off-by: Derek McGowan <derek@mcgstyle.net>

content/content.go

@@ -29,11 +29,11 @@ type Ingester interface {
 // TODO(stevvooe): Consider a very different name for this struct. Info is way
 // to general. It also reads very weird in certain context, like pluralization.
 type Info struct {
-	Digest      digest.Digest
-	Size        int64
-	CommittedAt time.Time
-	UpdatedAt   time.Time
-	Labels      map[string]string
+	Digest    digest.Digest
+	Size      int64
+	CreatedAt time.Time
+	UpdatedAt time.Time
+	Labels    map[string]string
 }
 
 type Status struct {

content/store.go

@@ -52,10 +52,10 @@ func (s *store) Info(ctx context.Context, dgst digest.Digest) (Info, error) {
 
 func (s *store) info(dgst digest.Digest, fi os.FileInfo) Info {
 	return Info{
-		Digest:      dgst,
-		Size:        fi.Size(),
-		CommittedAt: fi.ModTime(),
-		UpdatedAt:   fi.ModTime(),
+		Digest:    dgst,
+		Size:      fi.Size(),
+		CreatedAt: fi.ModTime(),
+		UpdatedAt: fi.ModTime(),
 	}
 }