Issue #449 - Tests for g to GitHub issues functionality

r? @tagawa 

Pretty simple stuff. Just making sure we can find the right elements on the github issues page after pressing g. In the future it might be nice to check that the `repoPath` matches the URL on GitHub, but I can't figure out how to do that right now. (Looking at https://theintern.github.io/leadfoot/Command.html#execute but those docs sort of confuse me. >_>)