Update module name to github.com/stellar/throttled

[leighmcculloch]

Summary

Update module name to github.com/stellar/throttled.

Goal and scope

@MonsieurNicolas made the suggestion stellar/go#1642 (comment) that we should take @bartekn's into the @stellar org. He setup the project and I pushed the master branch from over there. This change updates the imports and package name internally so that it knows itself at this repo address.

Related to stellar/go#1634

[leighmcculloch]

The builds pass on the latest version of Go but not the myriad of older versions of Go which is understandable.

[leighmcculloch]

There's quite a few things in the build scripts that need updating, but it passes on Go 1.12, and this code is code we're already importing in it's current state, so I think we should merge this even though the other builds are failing, and then discuss how much we want to invest in cleaning up this repo.

[leighmcculloch]

I fixed the TravisCI config in #2. Those changes are temporarily showing up in this diff because I merged the config into this branch to check that the tests pass with these changes. After #2 is merged this PRs diff will be smaller.

[tomquisel]

Looks good! Why isn't the Makefile needed?

[leighmcculloch]

Travis knows how to build and test go projects without any configuration. The makefile was causing travis to run make install, and the makefile contained unnecessary go get commands. Since we rely on using straight up go commands in our other repos and the makefile contained about 50% things that we don't need, I figured it was better to drop it in our diverged fork than to spend time cleaning it up.