change pubkey type in Signer interface from ecdsa.PublicKey to []byte

Signed-off-by: Daisuke Kanda <[email protected]>

core/signer.go

@@ -1,8 +1,6 @@
 package core
 
 import (
-	"crypto/ecdsa"
-
 	"github.com/cosmos/gogoproto/proto"
 )
 
@@ -14,5 +12,5 @@ type SignerConfig interface {
 
 type Signer interface {
 	Sign(digest []byte) (signature []byte, err error)
-	GetPublicKey() (ecdsa.PublicKey, error)
+	GetPublicKey() ([]byte, error)
 }