Update development APNS host (#146)

* Update development APNS host

The development APNS host url was outdated.
The new URL is `https://api.sandbox.push.apple.com`
From: https://developer.apple.com/documentation/usernotifications/setting_up_a_remote_notification_server/sending_notification_requests_to_apns

Author: sideshow

client.go

@@ -19,7 +19,7 @@ import (
 
 // Apple HTTP/2 Development & Production urls
 const (
-	HostDevelopment = "https://api.development.push.apple.com"
+	HostDevelopment = "https://api.sandbox.push.apple.com"
 	HostProduction  = "https://api.push.apple.com"
 )
 

client_test.go

@@ -58,22 +58,22 @@ func (c *mockTransport) CloseIdleConnections() {
 
 func TestClientDefaultHost(t *testing.T) {
 	client := apns.NewClient(mockCert())
-	assert.Equal(t, "https://api.development.push.apple.com", client.Host)
+	assert.Equal(t, "https://api.sandbox.push.apple.com", client.Host)
 }
 
 func TestTokenDefaultHost(t *testing.T) {
 	client := apns.NewTokenClient(mockToken()).Development()
-	assert.Equal(t, "https://api.development.push.apple.com", client.Host)
+	assert.Equal(t, "https://api.sandbox.push.apple.com", client.Host)
 }
 
 func TestClientDevelopmentHost(t *testing.T) {
 	client := apns.NewClient(mockCert()).Development()
-	assert.Equal(t, "https://api.development.push.apple.com", client.Host)
+	assert.Equal(t, "https://api.sandbox.push.apple.com", client.Host)
 }
 
 func TestTokenClientDevelopmentHost(t *testing.T) {
 	client := apns.NewTokenClient(mockToken()).Development()
-	assert.Equal(t, "https://api.development.push.apple.com", client.Host)
+	assert.Equal(t, "https://api.sandbox.push.apple.com", client.Host)
 }
 
 func TestClientProductionHost(t *testing.T) {