Add social media URL to podspec
Add social media URL to podspec

- Points to our Spotify Engineering Twitter account.

chrisbtreats/SPTPersistentCache,FootballAddicts/SPTPersistentCache,chrisbtreats/SPTPersistentCache,FootballAddicts/SPTPersistentCache,spotify/SPTPersistentCache,FootballAddicts/SPTPersistentCache,chrisbtreats/SPTPersistentCache,spotify/SPTPersistentCache,FootballAddicts/SPTPersistentCache,spotify/SPTPersistentCache,chrisbtreats/SPTPersistentCache