Function isBoolean

src/lib/coerce.js:91–91

        otherOpts: ['dflt', 'arrayOk'],
        coerceFunction: function(v, propOut, dflt, opts) {
            const isBoolean = value => value === true || value === false;
            if (isBoolean(v) || (opts.arrayOk && Array.isArray(v) && v.length > 0 && v.every(isBoolean))) {
                propOut.set(v);
            } else {