Added support for IP field on source creation. (#77)

## Description

Added support for IP field on source creation.

Sample code
```
package main

import (
	"log"

	"github.com/omise/omise-go"
	"github.com/omise/omise-go/operations"
)

const (
	// Read these from environment variables or configuration files!
	OmisePublicKey = "<PKEY>"
	OmiseSecretKey = "<SKEY>"
)

func main() {
	client, e := omise.NewClient(OmisePublicKey, OmiseSecretKey)
	if e != nil {
		log.Fatal(e)
	}

	// Creates a source from the token
	source, createSource := &omise.Source{}, &operations.CreateSource{
		Amount:   100000, // ฿ 1,000.00
		Currency: "thb",
		Type:     "wechat_pay",
		Ip:       "192.168.1.1",
	}
	if e := client.Do(source, createSource); e != nil {
		log.Fatal(e)
	}

	log.Printf("source: %s  amount: %s %d\n", source.ID, source.Currency, source.Amount)
	log.Printf("IP: %s\n", source.Ip)
}
```
 
## Rollback procedure

`default rollback procedure`

---------

Co-authored-by: Aashish <[email protected]>

operations/source.go

@@ -16,7 +16,6 @@ import (
 //	}
 //
 //	fmt.Println("created source:", source.ID)
-//
 type CreateSource struct {
 	Type                     string `json:"type"`
 	Amount                   int64  `json:"amount"`
@@ -32,6 +31,7 @@ type CreateSource struct {
 	TerminalID               string `json:"terminal_id,omitempty"`
 	ZeroInterestInstallments bool   `json:"zero_interest_installments,omitempty"`
 	PlatformType             string `json:"platform_type,omitempty"`
+	Ip                       string `json:"ip,omitempty"`
 }
 
 func (req *CreateSource) Describe() *internal.Description {
@@ -52,7 +52,6 @@ func (req *CreateSource) Describe() *internal.Description {
 //	}
 //
 //	fmt.Printf("source #123: %#v\n", source)
-//
 type RetrieveSource struct {
 	SourceID string `json:"-"`
 }

operations/source_test.go

@@ -56,3 +56,22 @@ func TestCreateSourceWithPlatformType(t *testing.T) {
 	client.MustDo(exampleSource, createSource)
 	r.Equal(t, SourceID, exampleSource.ID)
 }
+
+func TestCreateSourceWithIP(t *testing.T) {
+	const (
+		SourceID = "src_test_5mygxph6d55vvy8nn9i"
+		Ip       = "192.168.1.1"
+	)
+	client := testutil.NewFixedClient(t)
+
+	exampleSource, createSource := &omise.Source{}, &operations.CreateSource{
+		Type:     "wechat_pay",
+		Amount:   20000,
+		Currency: "thb",
+		Ip:       Ip,
+	}
+
+	client.MustDo(exampleSource, createSource)
+	r.Equal(t, SourceID, exampleSource.ID)
+	r.Equal(t, Ip, exampleSource.Ip)
+}

source.go

@@ -12,4 +12,5 @@ type Source struct {
 	References               *References    `json:"references"`
 	ZeroInterestInstallments bool           `json:"zero_interest_installments"`
 	PlatformType             string         `json:"platform_type"`
+	Ip                       string         `json:"ip"`
 }

testdata/fixtures/api.omise.co/sources-post.json

@@ -10,6 +10,7 @@
   "currency": "MYR",
   "email": "[email protected]",
   "flow": "redirect",
+  "ip": "192.168.1.1",
   "installment_term": null,
   "name": null,
   "mobile_number": null,