[BUG] Unexpected backslashes in forwarded messages

**Describe the bug**
When EFB forward a message from ETM to EWS, under some circumstances there will be unexpected backslashes in messages in WeChat.

**To Reproduce**
Steps to reproduce the behavior:
1. Set up EFB to sync messages between Telegram and WeChat
2. Send a message in Telegram with the following content:
```
URL
---------------
```
where `URL` is a URL with address `tg://user?id=629325599`

Now the message is forwarded to WeChat, but its content is strange:

```
[URL](tg://user?id=629325599)
\- \- \- \- \- \- \- \- \- \- \- \- \- \- \-
```

**Expected behavior**
The message forwarded to WeChat should be something like:

```
[URL](tg://user?id=629325599)
---------------
```

or

```
URL
---------------
```

**Version information (please complete the following information):**
- OS: Ubuntu 20.04.1 LTS x86_64
- Detailed Python, EFB and module versions:

```
EH Forwarder Bot
Version: 2.1.0
Python version:
3.8.5 (default, Jul 28 2020, 12:59:40)
[GCC 9.3.0]
Running on profile "wechat2tg".

Master channel:
Telegram Master (blueset.telegram) 2.2.3 # Default instance

Slave channel:
WeChat Slave (blueset.wechat) 2.0.4 # Default instance

Middleware:
Search Message Middleware (catbaron.search_msg) 0.1.0 # Default instance
```

**Additional context**
If we downgrade efb-telegram-master from 2.2.3 to 2.2.2, everything goes OK.