layer: format code with gofumpt

Formatting the code with https://github.com/mvdan/gofumpt

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

layer/layer.go

@@ -174,12 +174,10 @@ type Store interface {
 	Get(ChainID) (Layer, error)
 	Map() map[ChainID]Layer
 	Release(Layer) ([]Metadata, error)
-
 	CreateRWLayer(id string, parent ChainID, opts *CreateRWLayerOpts) (RWLayer, error)
 	GetRWLayer(id string) (RWLayer, error)
 	GetMountID(id string) (string, error)
 	ReleaseRWLayer(RWLayer) ([]Metadata, error)
-
 	Cleanup() error
 	DriverStatus() [][2]string
 	DriverName() string