fix comments

credentials/credentials.go

@@ -71,7 +71,7 @@ type Credentials interface {
 }
 
 // TransportAuthenticator defines the common interface for all the live gRPC wire
-// protocol and supported transport security protocols (e.g., TLS, SSL).
+// protocols and supported transport security protocols (e.g., TLS, SSL).
 type TransportAuthenticator interface {
 	// Handshake does the authentication handshake specified by the corresponding
 	// authentication protocol on rawConn.