Update Travis Xcode image to 7.3
Update Travis Xcode image to 7.3

kumabook/XCDYouTubeKit,twobitlabs/XCDYouTubeKit,mingsai/XCDYouTubeVideoPlayerViewController,creationst/XCDYouTubeKit,gshaviv/XCDYouTubeVideoPlayerViewController,c0unt0/XCDYouTubeKit,twobitlabs/XCDYouTubeKit,morrisirrom/XCDYouTubeKit,0xced/XCDYouTubeKit,c0unt0/XCDYouTubeKit,mingsai/XCDYouTubeVideoPlayerViewController,gshaviv/XCDYouTubeVideoPlayerViewController,creationst/XCDYouTubeKit,kumabook/XCDYouTubeKit,gshaviv/XCDYouTubeVideoPlayerViewController,c0unt0/XCDYouTubeKit,creationst/XCDYouTubeKit,c0unt0/XCDYouTubeKit,gshaviv/XCDYouTubeVideoPlayerViewController,itamaker/XCDYouTubeKit,0xced/XCDYouTubeKit,kumabook/XCDYouTubeKit,kumabook/XCDYouTubeKit,morrisirrom/XCDYouTubeKit,mingsai/XCDYouTubeVideoPlayerViewController,gshaviv/XCDYouTubeVideoPlayerViewController,mingsai/XCDYouTubeVideoPlayerViewController,kumabook/XCDYouTubeKit,morrisirrom/XCDYouTubeKit,morrisirrom/XCDYouTubeKit,0xced/XCDYouTubeKit,twobitlabs/XCDYouTubeKit,0xced/XCDYouTubeKit,twobitlabs/XCDYouTubeKit,kumabook/XCDYouTubeKit,morrisirrom/XCDYouTubeKit,itamaker/XCDYouTubeKit,creationst/XCDYouTubeKit,gshaviv/XCDYouTubeVideoPlayerViewController,c0unt0/XCDYouTubeKit