ignore EOF error when json decoding empty response

In particular, this handles the case of trying to decode No Content
(204) responses.

github/github.go

@@ -332,6 +332,9 @@ func (c *Client) Do(req *http.Request, v interface{}) (*Response, error) {
 			io.Copy(w, resp.Body)
 		} else {
 			err = json.NewDecoder(resp.Body).Decode(v)
+			if err == io.EOF {
+				err = nil // ignore EOF errors caused by empty response body
+			}
 		}
 	}
 	return response, err

github/github_test.go

@@ -430,6 +430,24 @@ func TestDo_rateLimit_errorResponse(t *testing.T) {
 	}
 }
 
+func TestDo_noContent(t *testing.T) {
+	setup()
+	defer teardown()
+
+	mux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusNoContent)
+	})
+
+	var body json.RawMessage
+
+	req, _ := client.NewRequest("GET", "/", nil)
+	_, err := client.Do(req, &body)
+
+	if err != nil {
+		t.Fatalf("Do returned unexpected error: %v", err)
+	}
+}
+
 func TestSanitizeURL(t *testing.T) {
 	tests := []struct {
 		in, want string