Delay operation termination on cancel
Delay operation termination on cancel

Hopefully this will solve this crash observed on Travis: https://travis-ci.org/0xced/XCDYouTubeKit/jobs/85190012#L1895-L1896

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