Implemented exportChatInviteLink method

Author: acran

README.md

@@ -70,6 +70,7 @@ editMessageCaption
 editMessageReplyMarkup
 kickChatMember
 unbanChatMember
+exportChatInviteLink
 leaveChat
 getChat
 getChatAdministrators

lib/telegram-bot.js

@@ -1575,6 +1575,34 @@ var TelegramApi = function (params)
         }).nodeify(cb);
     };
 
+    /**
+     * METHOD: exportChatInviteLink
+     * PARAMS:
+     *      chat_id                     Unique identifier for the target chat or username of the target channel — User or GroupChat id
+     */
+    this.exportChatInviteLink = function (params, cb) {
+        var args = {};
+
+        if (params.chat_id !== undefined) args.chat_id = params.chat_id;
+
+        return new Promise(function(resolve, reject) {
+            _rest({
+                method: 'POST',
+                json: true,
+                formData: args,
+                uri: _baseurl + 'exportChatInviteLink'
+            })
+                .then(function(body) {
+                    return commonResponseHandler(body);
+                })
+                .then(function(data) {
+                    resolve(data);
+                })
+                .catch(function(err) {
+                    reject(err);
+                });
+        }).nodeify(cb);
+    };
 
     /**
      * METHOD: deleteMessage