bump google.golang.org/grpc v1.23.0

full diff: https://github.com/grpc/grpc-go/compare/v1.20.1...v1.23.0

This update contains security fixes:

- transport: block reading frames when too many transport control frames are queued (grpc/grpc-go#2970)
  - Addresses CVE-2019-9512 (Ping Flood), CVE-2019-9514 (Reset Flood), and CVE-2019-9515 (Settings Flood).

Other changes can be found in the release notes:
https://github.com/grpc/grpc-go/releases/tag/v1.23.0

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

vendor/google.golang.org/grpc/credentials/credentials.go

@@ -278,24 +278,22 @@ type ChannelzSecurityValue interface {
 // TLSChannelzSecurityValue defines the struct that TLS protocol should return
 // from GetSecurityValue(), containing security info like cipher and certificate used.
 type TLSChannelzSecurityValue struct {
+	ChannelzSecurityValue
 	StandardName      string
 	LocalCertificate  []byte
 	RemoteCertificate []byte
 }
 
-func (*TLSChannelzSecurityValue) isChannelzSecurityValue() {}
-
 // OtherChannelzSecurityValue defines the struct that non-TLS protocol should return
 // from GetSecurityValue(), which contains protocol specific security info. Note
 // the Value field will be sent to users of channelz requesting channel info, and
 // thus sensitive info should better be avoided.
 type OtherChannelzSecurityValue struct {
+	ChannelzSecurityValue
 	Name  string
 	Value proto.Message
 }
 
-func (*OtherChannelzSecurityValue) isChannelzSecurityValue() {}
-
 var cipherSuiteLookup = map[uint16]string{
 	tls.TLS_RSA_WITH_RC4_128_SHA:                "TLS_RSA_WITH_RC4_128_SHA",
 	tls.TLS_RSA_WITH_3DES_EDE_CBC_SHA:           "TLS_RSA_WITH_3DES_EDE_CBC_SHA",