Update apppreferences.js

[kmd-jamesgauld]

When building I received an "Unexpected token &&" error which, as far as I can tell, is a result of the following lines:

if (successCallback !== undefined
        && typeof successCallback !== function && typeof errorCallback !== function
        && dict === undefined && key === undefined
        && promiseLib
    )

The proposed change encapsulates the 'function' typeof checks in quotes to fix the fault.