Updated Travis CI config to xcode 8.3 image
Updated Travis CI config to xcode 8.3 image

Also removed broken matrix notifications and unnecessary `pod repo update` script.

Eitot/vienna-rss,josh64x2/vienna-rss,lapcat/vienna-rss,ViennaRSS/vienna-rss,josh64x2/vienna-rss,barijaona/vienna-rss,barijaona/vienna-rss,lapcat/vienna-rss,Eitot/vienna-rss,barijaona/vienna-rss,josh64x2/vienna-rss,lapcat/vienna-rss,lapcat/vienna-rss,ViennaRSS/vienna-rss,ViennaRSS/vienna-rss,barijaona/vienna-rss,josh64x2/vienna-rss,Eitot/vienna-rss,ViennaRSS/vienna-rss,barijaona/vienna-rss,ViennaRSS/vienna-rss,josh64x2/vienna-rss,Eitot/vienna-rss