Added a test that type checks the .tz() function
Added a test that type checks the .tz() function

mcliment/DefinitelyTyped,georgemarshall/DefinitelyTyped,AgentME/DefinitelyTyped,rolandzwaga/DefinitelyTyped,AgentME/DefinitelyTyped,borisyankov/DefinitelyTyped,AgentME/DefinitelyTyped,rolandzwaga/DefinitelyTyped,magny/DefinitelyTyped,dsebastien/DefinitelyTyped,borisyankov/DefinitelyTyped,georgemarshall/DefinitelyTyped,AgentME/DefinitelyTyped,georgemarshall/DefinitelyTyped,magny/DefinitelyTyped,dsebastien/DefinitelyTyped,georgemarshall/DefinitelyTyped,markogresak/DefinitelyTyped,one-pieces/DefinitelyTyped