Update ggcr (ko-build#113)

Mostly to pick up media type mutation, but this includes a bunch of
other fixes.

google/go-containerregistry@ff1ac7f...73724ba

go.mod

@@ -3,24 +3,23 @@ module github.com/google/ko
 go 1.12
 
 require (
-	github.com/docker/docker v1.4.2-0.20180531152204-71cd53e4a197
+	github.com/docker/docker v1.4.2-0.20190924003213-a8608b5b67c7
 	github.com/dprotaso/go-yit v0.0.0-20191028211022-135eb7262960
 	github.com/evanphx/json-patch v4.2.0+incompatible // indirect
 	github.com/fsnotify/fsnotify v1.4.7
 	github.com/google/btree v1.0.0 // indirect
 	github.com/google/go-cmp v0.2.0
-	github.com/google/go-containerregistry v0.0.0-20191002200252-ff1ac7f97758
+	github.com/google/go-containerregistry v0.0.0-20191209173213-73724ba06bda
 	github.com/gregjones/httpcache v0.0.0-20190212212710-3befbb6ad0cc // indirect
 	github.com/imdario/mergo v0.3.5 // indirect
 	github.com/mattmoor/dep-notify v0.0.0-20190205035814-a45dec370a17
-	github.com/modern-go/reflect2 v1.0.1 // indirect
 	github.com/spf13/afero v1.2.1 // indirect
 	github.com/spf13/cobra v0.0.5
 	github.com/spf13/jwalterweatherman v1.1.0 // indirect
 	github.com/spf13/pflag v1.0.5
 	github.com/spf13/viper v1.3.2
 	golang.org/x/sync v0.0.0-20190423024810-112230192c58
-	golang.org/x/tools v0.0.0-20191001184121-329c8d646ebe
+	golang.org/x/tools v0.0.0-20191206204035-259af5ff87bd
 	gopkg.in/yaml.v3 v3.0.0-20191026110619-0b21df46bc1d
 	k8s.io/apimachinery v0.0.0-20180904193909-def12e63c512
 	k8s.io/client-go v8.0.0+incompatible // indirect