Some problems with installation

[vinyvicente]

`$ composer require threadmeup/slack-sdk dev-master
./composer.json has been updated
Loading composer repositories with package information
Updating dependencies (including require-dev)
Package operations: 3 installs, 0 updates, 0 removals

• Installing symfony/event-dispatcher (2.8.x-dev 88b65f0) Cloning 88b65f0ac2 from cache
• Installing guzzle/guzzle (dev-master f7778ed) Cloning f7778ed85e from cache
• Installing threadmeup/slack-sdk (dev-master 77857d9) Cloning 77857d9 from cache
  symfony/event-dispatcher suggests installing symfony/dependency-injection ()
  symfony/event-dispatcher suggests installing symfony/http-kernel ()
  Package guzzle/guzzle is abandoned, you should avoid using it. Use guzzlehttp/guzzle instead.
  Package threadmeup/slack-sdk is abandoned, you should avoid using it. No replacement was suggested.`

Follow this:

Package guzzle/guzzle is abandoned, you should avoid using it. Use guzzlehttp/guzzle instead.
Package threadmeup/slack-sdk is abandoned, you should avoid using it. No replacement was suggested.

[vinyvicente]

Added pull request to this.