Fixed the error that was causing the Travis builds to fail
Fixed the error that was causing the Travis builds to fail

The issue was: since CocoaPods 0.38.0, the way pod headers are created on disk changed (see for example https://github.com/core-plot/core-plot/issues/204). This caused the webp/decode.h file to be unaccessible from CocoaPods installations. We could not change the import to libwebp/webp/decode.h since our git clone installation would then fail (as the path for that is Vendors/libwebp/src/webp). The solution was to rely on the COCOAPODS macro to make 2 different imports for Cocoapods and the other installation type.

tualatrix/SDWebImage,awkward/SDWebImage,geoffmacd/SDWebImage,twobitlabs/SDWebImage,smyrgl/SDWebImage,ikesyo/SDWebImage,Insfgg99x/SDWebImage,awkward/SDWebImage,HannaLu/SDWebImage,ttgb/SDWebImage,mattjgalloway/SDWebImage,klundberg/SDWebImage,yunzhongyoulong/SDWebImage,dreampiggy/SDWebImage,heroims/SDWebImage,altrooz/SDWebImage,amyhametov/SDWebImage,Kekanto/SDWebImage,iMinichrispy/SDWebImage,odyth/SDWebImage,dreampiggy/SDWebImage,dpettigrew/SDWebImage,Frntbac/SDWebImage,smule/SDWebImage,dreampiggy/SDWebImage,buleSky111/SDWebImage,iheartradio/SDWebImage,awkward/SDWebImage,zhang-yawei/SDWebImage,iosnatarajan/SDWebImage,rs/SDWebImage,ruaho/SDWebImage,tokorom/SDWebImage,cochat/SDWebImage,zllbird/SDWebImage,bpoplauschi/SDWebImage