Merge pull request #134 from spotify/remove-spotify-slack

Remove references to Spotify FOSS Slack

README.md

@@ -5,7 +5,6 @@
 [![License](https://img.shields.io/github/license/spotify/SPTPersistentCache.svg)](LICENSE)
 [![CocoaPods](https://img.shields.io/cocoapods/v/SPTPersistentCache.svg)](https://cocoapods.org/?q=SPTPersistentCache)
 [![Carthage compatible](https://img.shields.io/badge/Carthage-compatible-4BC51D.svg?style=flat)](https://github.com/Carthage/Carthage)
-[![Spotify FOSS Slack](https://slackin.spotify.com/badge.svg)](https://slackin.spotify.com)
 [![Readme Score](http://readme-score-api.herokuapp.com/score.svg?url=https://github.com/spotify/sptpersistentcache)](http://clayallsopp.github.io/readme-score?url=https://github.com/spotify/sptpersistentcache)
 
 Everyone tries to implement a cache at some point in their app’s lifecycle, and this is ours. This is a library that allows people to cache `NSData` with time to live (TTL) values and semantics for disk management.