Expose nextTick for API parity with abstract-leveldown

Author: vweevers

lib/levelup.js

@@ -325,6 +325,9 @@ LevelUP.prototype.toString = function () {
 
 LevelUP.prototype.type = 'levelup'
 
+// Expose nextTick for API parity with abstract-leveldown
+LevelUP.prototype._nextTick = nextTick
+
 function maybeError (db, callback) {
   if (!db.isOperational()) {
     nextTick(callback, new ReadError('Database is not open'))