delete context issue

[abhikchakraborty]

Hi looks like there is a small issue on delete context end point

https://github.com/dialogflow/dialogflow-nodejs-client/blob/master/module/delete_contexts_request.js#L47

var contextPath = this.context ? '/' + context : '';

Should be

var contextPath = this.context ? '/' + this.context : '';

Could you please do a new release with the fix.
Thanks !!

[abhikchakraborty]

Just saw that there is a PR #91 on this.
It would be great to have this working.