* Move DoRequest* to godo package with stdlib context
* Use stdlib context package in place of godo context.
* Remove Go 1.6 from TravisCI configuration.
* Use stdlib context in util and tests instead of godo context.
* Add in Go 1.8, 1.9, and 1.10 to TravisCI configuration.
* Put 1.10 in quotes.
This patch updates the godo package to use a portable Go context -- a
Context that works with Go versions prior to Go 1.7 as well as Go 1.7
and onwards.
Collin Shoop