Update CHANGELOG for version 2.6.0
Update CHANGELOG for version 2.6.0

twobitlabs/XCDYouTubeKit,creationst/XCDYouTubeKit,mingsai/XCDYouTubeVideoPlayerViewController,twobitlabs/XCDYouTubeKit,0xced/XCDYouTubeKit,creationst/XCDYouTubeKit,mingsai/XCDYouTubeVideoPlayerViewController,creationst/XCDYouTubeKit,mingsai/XCDYouTubeVideoPlayerViewController,0xced/XCDYouTubeKit,twobitlabs/XCDYouTubeKit,mingsai/XCDYouTubeVideoPlayerViewController,0xced/XCDYouTubeKit,twobitlabs/XCDYouTubeKit,creationst/XCDYouTubeKit,0xced/XCDYouTubeKit