Allow for updating EmailBlacklisted field

This is a dirty workaround for the problem with Golang empty values
and marshaling to JSON. The problem was described here:

https://willnorris.com/2014/05/go-rest-apis-and-pointers/

In this library all struct's fields should be pointers, not simple types
like `bool` or `string` because we can't say whether a value is empty
and we should omit it (`omitempty` field tag) or not.

This library is auto-generated by swagger codegen, and developers created
an issue for this problem:
swagger-api/swagger-codegen#7391

In this pull request we dirty fix our problem with only one field we want
to update (set value to false)

go.mod

@@ -1,4 +1,4 @@
-module github.com/sendinblue/APIv3-go-library
+module github.com/ghostery/APIv3-go-library
 
 go 1.16
 

lib/model_update_contact.go

@@ -1,7 +1,7 @@
 /*
  * SendinBlue API
  *
- * SendinBlue provide a RESTFul API that can be used with any languages. With this API, you will be able to :   - Manage your campaigns and get the statistics   - Manage your contacts   - Send transactional Emails and SMS   - and much more...  You can download our wrappers at https://github.com/orgs/sendinblue  **Possible responses**   | Code | Message |   | :-------------: | ------------- |   | 200  | OK. Successful Request  |   | 201  | OK. Successful Creation |   | 202  | OK. Request accepted |   | 204  | OK. Successful Update/Deletion  |   | 400  | Error. Bad Request  |   | 401  | Error. Authentication Needed  |   | 402  | Error. Not enough credit, plan upgrade needed  |   | 403  | Error. Permission denied  |   | 404  | Error. Object does not exist |   | 405  | Error. Method not allowed  |   | 406  | Error. Not Acceptable  | 
+ * SendinBlue provide a RESTFul API that can be used with any languages. With this API, you will be able to :   - Manage your campaigns and get the statistics   - Manage your contacts   - Send transactional Emails and SMS   - and much more...  You can download our wrappers at https://github.com/orgs/sendinblue  **Possible responses**   | Code | Message |   | :-------------: | ------------- |   | 200  | OK. Successful Request  |   | 201  | OK. Successful Creation |   | 202  | OK. Request accepted |   | 204  | OK. Successful Update/Deletion  |   | 400  | Error. Bad Request  |   | 401  | Error. Authentication Needed  |   | 402  | Error. Not enough credit, plan upgrade needed  |   | 403  | Error. Permission denied  |   | 404  | Error. Object does not exist |   | 405  | Error. Method not allowed  |   | 406  | Error. Not Acceptable  |
  *
  * API version: 3.0.0
  * Contact: [email protected]
@@ -13,7 +13,7 @@ type UpdateContact struct {
 	// Pass the set of attributes to be updated. These attributes must be present in your account. To update existing email address of a contact with the new one please pass EMAIL in attribtes. For example, `{ \"EMAIL\":\"[email protected]\", \"FNAME\":\"Ellie\", \"LNAME\":\"Roger\"}`. Keep in mind transactional attributes can be updated the same way as normal attributes. Mobile Number in \"SMS\" field should be passed with proper country code. For example {\"SMS\":\"+91xxxxxxxxxx\"} or {\"SMS\":\"0091xxxxxxxxxx\"}
 	Attributes *interface{} `json:"attributes,omitempty"`
 	// Set/unset this field to blacklist/allow the contact for emails (emailBlacklisted = true)
-	EmailBlacklisted bool `json:"emailBlacklisted,omitempty"`
+	EmailBlacklisted bool `json:"emailBlacklisted"`
 	// Set/unset this field to blacklist/allow the contact for SMS (smsBlacklisted = true)
 	SmsBlacklisted bool `json:"smsBlacklisted,omitempty"`
 	// Ids of the lists to add the contact to