test(mockDOMSource): fix tests using instanceof
test(mockDOMSource): fix tests using instanceof

staltz/cycle,usm4n/cyclejs,ntilwalli/cyclejs,cyclejs/cyclejs,usm4n/cyclejs,maskinoshita/cyclejs,feliciousx-open-source/cyclejs,ntilwalli/cyclejs,ntilwalli/cyclejs,feliciousx-open-source/cyclejs,usm4n/cyclejs,feliciousx-open-source/cyclejs,feliciousx-open-source/cyclejs,maskinoshita/cyclejs,cyclejs/cycle-core,cyclejs/cyclejs,ntilwalli/cyclejs,maskinoshita/cyclejs,usm4n/cyclejs,cyclejs/cycle-core,staltz/cycle,maskinoshita/cyclejs,cyclejs/cyclejs,cyclejs/cyclejs