Rocket.Chat improperly parses a diff with Markdown code in it

Description:

To reproduce the issue, paste the following text in a Rocket.Chat message:

``` diff
martin.mein-iserv.de ~ # diff -u test.txt test2.txt 
--- test.txt    2018-04-16 16:16:44.009313579 +0200
+++ test2.txt   2018-04-16 16:16:58.970366447 +0200
@@ -1 +1,7 @@
 This is a test.
+
+```
+some markdown code
+```
+
+This is another test line.
```

Normal Markdown parsers would display the result like this:

martin.mein-iserv.de ~ # diff -u test.txt test2.txt 
--- test.txt    2018-04-16 16:16:44.009313579 +0200
+++ test2.txt   2018-04-16 16:16:58.970366447 +0200
@@ -1 +1,7 @@
 This is a test.
+
+```
+some markdown code
+```
+
+This is another test line.

Rocket.Chat instead displays it like this:

martin.mein-iserv.de ~ # diff -u test.txt test2.txt 
--- test.txt    2018-04-16 16:16:44.009313579 +0200
+++ test2.txt   2018-04-16 16:16:58.970366447 +0200
@@ -1 +1,7 @@
 This is a test.
+
+

+some markdown code
+

+
+This is another test line.

Apparently it interprets the ``` in the diff as Markdown, which it shouldn't.

Server Setup Information:

• Version of Rocket.Chat Server: 0.60.3
• Operating System: Debian stretch
• Deployment Method(snap/docker/tar/etc): tar
• Number of Running Instances: 1
• DB Replicaset Oplog: Disabled
• Node Version: v8.9.3
• mongoDB Version: mongodb-org 3.2.17

Reproduce the issue by sending the supplied diff as a Rocket.Chat message and compare the rendered output with the expected Markdown rendering. Trace the message Markdown parsing and rendering path, focusing on how triple backticks inside a diff block are handled. Done means the embedded code fences remain part of the diff and the surrounding message renders correctly.