Issue title: [BUG] Impossible to upload from library in a channel or DM
 Issue body: Uploads from library don't work in latest beta branch. Uploading through share extension works tho.

- Rocket.Chat app version: 3.0.0 (latest beta branch as of July 9th 2018)
- Rocket.Chat server version: 0.66.0
- Device (or Simulator) you're running with: iPhone X / iOS 11.4

**Steps to reproduce :**

1. Open channel or DM session
2. Tap "+", "Choose from library"
3. Tap any file / photo
4. Tap "Upload"

**Expected behavior :**

File uploads and appears in conversation.

**Actual behavior :**

Nothing happens (at least for me)
 Comments: 
 Comment 0: Xcode debug console shows that requests are indeed sent. But no payload ?

```
[REST][REQUEST]: https://{domain.com}/api/v1/rooms.upload/iTsYkQZMR9b6eNpzF: 
[REST][RESULT][https://{domain.com}/api/v1/rooms.upload/iTsYkQZMR9b6eNpzF]:
```
 Comment 1: @rafaelks Any idea why this happens ? Looks like all the changes regarding upload are in a specific branch ? Both current beta and develop have the problem. Just reproduced it on other devices too.
 Comment 2: Android client has trouble uploading too, throwing an error `Use JsonReader.setLenient(true) to accept malformed JSON at path $`. So it's probably server-related. Will investigate and close the issue if it's indeed on the server side.
 Comment 3: Solved by increasing `client_max_body_size` on nginx config, as provided on https://github.com/RocketChat/Rocket.Chat.Android/issues/1050. Closing now. Sorry for the false flag.
 Comment 4: Nice! 👍 
{'source': 'GithubIssues', 'repo_name_with_owner': 'RocketChat/Rocket.Chat.iOS', 'issue_id': 339519780, 'repo_stars': 1098.0}