Upgraded to elixir 1.0.0-rc2

FYI, waiting on pull requests in linguist and poison upgrading to 1.0.0-rc2 because this pull request should be merged so I can drop the references to my copies of those projects.

Also note that I resolved two warnings with the Module.concat function, versus calling Phoenix.Project.module_root.Router directly (don't know if that's a 1.0.0-rc2 warning or just something lying around).