function getLessThan(currentMediaType, breakpointOrder) {
    // get the ordering of the current media type
    const currentOrder = breakpointOrder[currentMediaType]

    return transform(breakpointOrder, (result, breakpoint, mediaType) => {
        // if the breakpoint is a number
        if (typeof breakpoint === 'number' && breakpointOrder[mediaType]) {
            // store whether or not it is less than the breakpoint
            result[mediaType] = currentOrder < breakpointOrder[mediaType]
            // handle non numerical breakpoints specially
        } else {
            result[mediaType] = false
        }
    })
}
Compute the `lessThan` object based on the browser width.
@arg {number} browserWidth - Width of the browser.
@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.