Switch from govendor to go modules. (#587)

Thanks to @BenoitKnecht for leading the way on this.

vendor/github.com/google/go-github/github/activity_events.go

@@ -15,7 +15,7 @@ import (
 // Event represents a GitHub event.
 type Event struct {
 	Type       *string          `json:"type,omitempty"`
-	Public     *bool            `json:"public"`
+	Public     *bool            `json:"public,omitempty"`
 	RawPayload *json.RawMessage `json:"payload,omitempty"`
 	Repo       *Repository      `json:"repo,omitempty"`
 	Actor      *User            `json:"actor,omitempty"`
@@ -32,6 +32,10 @@ func (e Event) String() string {
 // a value of the corresponding struct type will be returned.
 func (e *Event) ParsePayload() (payload interface{}, err error) {
 	switch *e.Type {
+	case "CheckRunEvent":
+		payload = &CheckRunEvent{}
+	case "CheckSuiteEvent":
+		payload = &CheckSuiteEvent{}
 	case "CommitCommentEvent":
 		payload = &CommitCommentEvent{}
 	case "CreateEvent":
@@ -56,6 +60,8 @@ func (e *Event) ParsePayload() (payload interface{}, err error) {
 		payload = &IssuesEvent{}
 	case "LabelEvent":
 		payload = &LabelEvent{}
+	case "MarketplacePurchaseEvent":
+		payload = &MarketplacePurchaseEvent{}
 	case "MemberEvent":
 		payload = &MemberEvent{}
 	case "MembershipEvent":