GoCenter doesn't support dynamic versions

[ankushchadha]

Steps to reproduce:

1. export GOPROXY=https://gocenter.io
2. go get github.com/0xAX/notificator@master

Actual output: go get fails with the following: invalid version: reading https://gocenter.io/github.com/0x%21a%21x/notificator/@v/master.info: 404 Not Found

Expected output: go get github.com/0xAX/notificator@master should be successful. Internally need to map the master to an actual version.

To help us debug your issue please confirm the following :

• [x] I’ve read the FAQ.
• [x] I’ve explained the steps to reproduce the error or the motivation/use case of the question/suggestion.
• [x] I’ve provided Go Module Name and Version (if applicable)

[elioengcomp]

This capability was added to GoCenter. Users can now fetch from GoCenter modules using the following request formats:

• go get <PATH>@<BRANCH>
• go get <PATH>@<COMMIT_HASH>

GoCenter will translate the request to the actual SemVer compatible version and serve that instead.