display error for failed get token

accessToken.go

@@ -34,6 +34,8 @@ func GetAccessToken() (string, error) {
 	if isAuthTokenExpired(t) {
 		t, err = renewAuthToken()
 		if err != nil {
+			log.Fatal("Cannot renew AccessToken from Wechat Server:")
+			log.Fatal(err)
 			return "", err // cannot get token
 		}
 	}