View on GitHub button does not link to right branch

Created by: felixfbecker

• Sourcegraph version: sourcegraph.com

Steps to reproduce:

1. Go to https://sourcegraph.sgdev.org/github.com/sourcegraph/sourcegraph@accounts or any other non-default branch in any repo
2. Click the GitHub button

Expected behavior:

Get taken to the branch on GitHub

Actual behavior:

Get taken to master