[BUG] Markdown parsing code adds a new line and parse image URLs

[rafaelks]

Description:

This issue is about two things in our Markdown parsing:

1. It adds a new line to the markdown processed HTML;
2. It renders the images of the links that are inside of the code block;

Server Setup Information:

• Version of Rocket.Chat Server: 0.62
• Operating System: Linux

Steps to Reproduce:

1. Send a new message with this text:

Here's the code block, remove the initial `\` in the begin and the end before sending the message.

\```
➜  ~  time wget https://open.rocket.chat/avatar/rafael.kellermann
--2018-02-28 09:58:41--  https://open.rocket.chat/avatar/rafael.kellermann
Resolving open.rocket.chat... 104.196.189.8
Connecting to open.rocket.chat|104.196.189.8|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: 10875 (11K) [image/jpeg]
Saving to: 'rafael.kellermann'

rafael.kellermann                      100%[===========================================================================>]  10.62K  --.-KB/s    in 0s      

2018-02-28 09:59:05 (30.1 MB/s) - 'rafael.kellermann' saved [10875/10875]


real	0m23.927s
user	0m0.023s
sys	0m0.020s
\```

Expected behavior:

1. It should not add a new line;
2. It should not render the images;

Actual behavior:

1. It adds a new line;
2. It renders the images;

[rafaelks]

@karlprieb Assigned to you, but not really sure who needs to be assigned.

[lunaticmonk]

@rafaelks @karlprieb If you don't mind, may I send a pull request?

[karlprieb]

@sumedh123 go ahead :)