documentdb: update _ts property type
documentdb: update _ts property type

_ts (retrieved from documentdb documents) is a number (not a string)
dsebastien/DefinitelyTyped,chrootsu/DefinitelyTyped,borisyankov/DefinitelyTyped,georgemarshall/DefinitelyTyped,AgentME/DefinitelyTyped,zuzusik/DefinitelyTyped,georgemarshall/DefinitelyTyped,magny/DefinitelyTyped,magny/DefinitelyTyped,arusakov/DefinitelyTyped,one-pieces/DefinitelyTyped,chrootsu/DefinitelyTyped,mcliment/DefinitelyTyped,zuzusik/DefinitelyTyped,arusakov/DefinitelyTyped,georgemarshall/DefinitelyTyped,alexdresko/DefinitelyTyped,alexdresko/DefinitelyTyped,AgentME/DefinitelyTyped,dsebastien/DefinitelyTyped,zuzusik/DefinitelyTyped,markogresak/DefinitelyTyped,georgemarshall/DefinitelyTyped,arusakov/DefinitelyTyped,rolandzwaga/DefinitelyTyped,borisyankov/DefinitelyTyped,AgentME/DefinitelyTyped,AgentME/DefinitelyTyped,rolandzwaga/DefinitelyTyped,laurentiustamate94/DefinitelyTyped