Update contributing guide

Fix parsing of flags in 'artillery quick'

* Remove whitespace
* Remove .gitattributes

* Vagrantfile updating gitignore
* adding global node modules
* adding git attributes
* Fixing gitattributes
* one more time
* changing to ubuntu

Issue 72 csv

(#29) - One Dino Per Day

Used the year, month, and day modulo the length of the dino art to
select the proper art for the day.  Use localized day.

Add brontosaurus and tyranosaurus.  Bug: not entirely aligned to
speech bubble.  Hoping no one was feeling married to the simple
dino art.

quick mode improvements

- add "-c" flag to specify a fixed number of arrivals
- add "-n" flag to specify the number of messages to send

https://github.com/shoreditch-ops/artillery/issues/54

Debugging friendly message shows parsing errors

Invalid file message is now adjusted to the file format.

Invalid file format message was always complaining about JSON even if the file was YAML.

Warn if using XPath capture but libxmljs is not installed