*: fix golint's omit type suggestions

pkg/core/transaction/attribute.go:67:14: should omit type uint8 from declaration of var urllen; it will be inferred from the right-hand side
pkg/crypto/keys/publickey.go:184:8: should omit type []byte from declaration of var b; it will be inferred from the right-hand side
pkg/network/payload/version_test.go:15:12: should omit type bool from declaration of var relay; it will be inferred from the right-hand side

Refs. #213.

pkg/core/transaction/attribute.go

@@ -64,7 +64,7 @@ func (attr *Attribute) EncodeBinary(w io.Writer) error {
 		Remark12, Remark13, Remark14, Remark15:
 		bw.WriteBytes(attr.Data)
 	case DescriptionURL:
-		var urllen uint8 = uint8(len(attr.Data))
+		var urllen = uint8(len(attr.Data))
 		bw.WriteLE(urllen)
 		fallthrough
 	case Script, ContractHash, Vote, Hash1,	Hash2, Hash3, Hash4, Hash5, Hash6,

pkg/crypto/keys/publickey.go

@@ -181,7 +181,7 @@ func (p *PublicKey) Signature() []byte {
 
 // Address returns a base58-encoded NEO-specific address based on the key hash.
 func (p *PublicKey) Address() string {
-	var b []byte = p.Signature()
+	var b = p.Signature()
 
 	b = append([]byte{0x17}, b...)
 	csum := hash.Checksum(b)

pkg/network/payload/version_test.go

@@ -12,7 +12,7 @@ func TestVersionEncodeDecode(t *testing.T) {
 	var id uint32 = 13337
 	useragent := "/NEO:0.0.1/"
 	var height uint32 = 100500
-	var relay bool = true
+	var relay = true
 
 	version := NewVersion(id, port, useragent, height, relay)