Mongo insert is deprecated

[chantorak]

Using mongo:

etl.file('test.csv')
  .pipe(etl.csv())
  .pipe(etl.collect(10))
  .pipe(etl.mongo.insert(collection));

Will result in:

(node:62919) DeprecationWarning: collection.insert is deprecated. Use insertOne, insertMany or bulkWrite instead.

[ZJONSSON]

Yes - so this still works but has to be updated. Do you mind taking a stab at a PR?

[chantorak]

#107