Use hasOwnProperty from Object prototype (Node v6.x)

[kashav]

Was running into an issue with hasOwnProperty:

TypeError: object.hasOwnProperty is not a function
    at cleanFieldNames (/.../node_modules/winston-mongodb/lib/helpers.js:41:17)
    at cleanFieldNames (/.../node_modules/winston-mongodb/lib/helpers.js:56:7)
    at cleanFieldNames (/.../node_modules/winston-mongodb/lib/helpers.js:56:7)
    at Object.exports.prepareMetaData (/.../node_modules/winston-mongodb/lib/helpers.js:18:5)
    at /.../node_modules/winston-mongodb/lib/winston-mongodb.js:263:28
    at Db.collection (/.../node_modules/mongodb/lib/db.js:449:20)
    at /.../node_modules/winston-mongodb/lib/winston-mongodb.js:253:16
    at _combinedTickCallback (internal/process/next_tick.js:67:7)
    at process._tickCallback (internal/process/next_tick.js:98:9)

Seems to be caused by a change in Node v6:

• https://github.com/nodejs/node/wiki/Breaking-changes-between-v5-and-v6#querystring
• querystring: don't inherit from Object.prototype nodejs/node#6055
• url: use "empty" object for empty query strings nodejs/node#6289

Updated to use hasOwnProperty from the Object prototype object instead.

[yurijmikhalevich]

Thank you for the fix.

[kashav]

Thanks for the quick merge + bump! 😄