Only undo '.' escaping in field names.

[alienth]

Fixes cases where content which is intended to be escaped, such as VCLs containing \., becomes clobbered, as described in #11.

[alienth]

For the following test:

package main

import (
        "fmt"
        "github.com/sethvargo/go-fastly"
)

func main() {
        client, _ := fastly.NewClient("foo")
        myvcl := "if (req.http.host ~ \"([[:alnum:]]+)\\.([[:alnum:]]+)$\") {"
        fmt.Println(myvcl)
        vcl, _ := client.UpdateVCL(&fastly.UpdateVCLInput{Name: "myvcl", Service: "abcdef0123456789", Version: "1", Content: myvcl})
        fmt.Println(vcl.Content)
}

Current output:

if (req.http.host ~ "([[:alnum:]]+)\.([[:alnum:]]+)$") {
if (req.http.host ~ "([[:alnum:]]+).([[:alnum:]]+)$") {

Output with changes in PR:

if (req.http.host ~ "([[:alnum:]]+)\.([[:alnum:]]+)$") {
if (req.http.host ~ "([[:alnum:]]+)\.([[:alnum:]]+)$") {