Update cocoapods version to latest

[alvincrisuy]

• [ ] I've read and understood the Contributing guidelines and have done my best effort to follow them.
• [ ] I've read and agree to the Code of Conduct.
• [ ] I've searched for any related issues and avoided creating a duplicate issue.

Description

e.g. Description of the bug or feature

Reproducible in:

• [ ] This is reproducible in the sample project. SlackTextViewController version: iOS version(s): Device(s):

Steps to reproduce:

Expected result:

e.g. What you expected to happen

Actual result:

e.g. What actually happened

Attachments:

e.g. Logs, screenshots, screencast, sample project, funny gif, etc.

[dzenbot]

The podspec is already targeting the latest release https://github.com/slackhq/SlackTextViewController/blob/master/SlackTextViewController.podspec#L1

We will soon submit a new version with iOS 11 fixes, but if you're eager of cloning the tip of master, you can always just do https://guides.cocoapods.org/using/the-podfile.html#from-a-podspec-in-the-root-of-a-library-repo