function getIs(currentMediaType, breakpoints) {
    return transform(breakpoints, (result, breakpoint, mediaType) => {
        // store whether or not the current media type matches the breakpoint in the mapping
        result[mediaType] = mediaType === currentMediaType
    })
}
Compute the `lessThan` object based on the browser width.
@arg {object} breakpoints - The breakpoints object.
@arg {currentMediaType} breakpoints - The curent media type.
@returns {object} The `lessThan` object.  Its keys are the same as the
keys of the breakpoints object.  The value for each key indicates whether
or not the browser width is less than the breakpoint.