forewarned: do not update devDep `taffydb` to 2.7.x until this bug is fixed

[GerHobbelt]

As I was messing around with jsdoc2md source, I ran into trouble: several unit tests failed, even on the original master branch, after I had updated the npm packages using npmu.

Turns out taffydb 2.7.x has a bug in its column: {isUndefined: true} logic, which is being used in a couple of jsdoc2md unit tests.

taffydb issue № 159: https://github.com/typicaljoe/taffydb/issues/159

This will be an issue for jsdoc2md once mainline decides to updated the devDependencies including taffydb: the latest taffydb release as of this writing (2.7.3) still exhibits the bug and thus causes about 6 jsdoc2md unit tests to fail because the {asdf:true} record does not get filtered out by taffydb following this jsdoc2md::jsdoc/util/templateHelper::helper.prune code:

exports.prune = data => {
...
    if (!env.opts.access || (env.opts.access && !env.opts.access.includes('all'))) {
...
        if (env.opts.access && !env.opts.access.includes('undefined')) {
            data({access: {isUndefined: true}}).remove();
        }
    }

    return data;
};