Fix backslash (\) issue in escape_markdown

[Artin-GH]

Fix backslash () issue in escape_markdown

When I was using backslash in telebot.formatting.escape_markdown, I was getting an error from the Telegram API.
The regex pattern inside the escape_markdown function was missing a backslash within the brackets.

[Badiboy]

Could you please provide usecase(s) where you got the error that will be fixed with your patch?

[Artin-GH]

from telebot import TeleBot
from telebot import types
from telebot.formatting import escape_markdown

tb = TeleBot('0000000000:AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA')

@tb.message_handler(commands=['start'])
def on_start(message: types.Message):
    tb.send_message(
        message.chat.id, '`{}`'.format(escape_markdown("A message that ends with \\")), 'MarkdownV2')

tb.infinity_polling(skip_pending=True)

You will get something like this when you run the code above and send "/start" to bot:

telebot.apihelper.ApiTelegramException: A request to the Telegram API was unsuccessful. Error code: 400. Description: Bad Request: can't parse entities: Can't find end of Code entity at byte offset 0
"

[Badiboy]

Thank you, looks reasonable.

@coder2020official It's your function - please, confirm update.

[coder2020official]

Sorry for a late response