Bump to v75
Bump to v75

* Preliminary [dep](https://github.com/golang/dep) support.
* Update tq to v0.5
* Add tq and dep to s3 to ease dep integration.
* Update go to 1.9.1 & 1.8.4 & default to them - https://groups.google.com/forum/#!msg/golang-nuts/sHfMg4gZNps/a-HDgDDDAAAJ

heroku/heroku-buildpack-go,heroku/heroku-buildpack-go