Add support for 451 status code

Fixes #306.

Change-Id: I3b42c946f8255e165c3bbd83b1566675d21fb0e8

github/github.go

@@ -366,6 +366,13 @@ type ErrorResponse struct {
 	Response *http.Response // HTTP response that caused this error
 	Message  string         `json:"message"` // error message
 	Errors   []Error        `json:"errors"`  // more detail on individual errors
+	// Block is only populated on certain types of errors such as code 451.
+	// See https://developer.github.com/changes/2016-03-17-the-451-status-code-is-now-supported/
+	// for more information.
+	Block *struct {
+		Reason    string     `json:"reason,omitempty"`
+		CreatedAt *Timestamp `json:"created_at,omitempty"`
+	} `json:"block,omitempty"`
 }
 
 func (r *ErrorResponse) Error() string {

github/github_test.go

@@ -520,7 +520,8 @@ func TestCheckResponse(t *testing.T) {
 		Request:    &http.Request{},
 		StatusCode: http.StatusBadRequest,
 		Body: ioutil.NopCloser(strings.NewReader(`{"message":"m",
-			"errors": [{"resource": "r", "field": "f", "code": "c"}]}`)),
+			"errors": [{"resource": "r", "field": "f", "code": "c"}],
+			"block": {"reason": "dmca", "created_at": "2016-03-17T15:39:46Z"}}`)),
 	}
 	err := CheckResponse(res).(*ErrorResponse)
 
@@ -532,6 +533,13 @@ func TestCheckResponse(t *testing.T) {
 		Response: res,
 		Message:  "m",
 		Errors:   []Error{{Resource: "r", Field: "f", Code: "c"}},
+		Block: &struct {
+			Reason    string     `json:"reason,omitempty"`
+			CreatedAt *Timestamp `json:"created_at,omitempty"`
+		}{
+			Reason:    "dmca",
+			CreatedAt: &Timestamp{time.Date(2016, 3, 17, 15, 39, 46, 0, time.UTC)},
+		},
 	}
 	if !reflect.DeepEqual(err, want) {
 		t.Errorf("Error = %#v, want %#v", err, want)