Add options argument to Batch#write

[vweevers]

levelup/lib/batch.js

Line 50 in c3845ee

Batch.prototype.write = function (callback) {

The argument can default to {} (so this is safe to release as a patch) and then passed to:

levelup/lib/batch.js

Line 61 in c3845ee

this.batch.write(function (err) {

Passing options to write has been supported in abstract-leveldown since forever: Level/abstract-leveldown@efbd19a