Add missing tests for imagemin.buffer
Add missing tests for imagemin.buffer

markogresak/DefinitelyTyped,AgentME/DefinitelyTyped,dsebastien/DefinitelyTyped,georgemarshall/DefinitelyTyped,AgentME/DefinitelyTyped,mcliment/DefinitelyTyped,borisyankov/DefinitelyTyped,borisyankov/DefinitelyTyped,AgentME/DefinitelyTyped,magny/DefinitelyTyped,magny/DefinitelyTyped,georgemarshall/DefinitelyTyped,georgemarshall/DefinitelyTyped,AgentME/DefinitelyTyped,georgemarshall/DefinitelyTyped,dsebastien/DefinitelyTyped