Return the correct urls from appveyor

[llrs]

Previously the appveyor badge was not properly rendered as appveyor_info returned the url of the repository as the image. The change only affects the name of the urls returned by appveyor_info to be used by use_badge_appveyor.

[jennybc]

Thanks!

I tested this locally and found another pre-existing problem. Want to fix it too while you're making this PR? Please make the url assignment look like this:

  url <- file.path(
    "https://ci.appveyor.com",
    "project",
    gh$username,
    gh$repo
  )

The "project" part needs to be added.

Also go ahead and add a NEWS bullet about this fix.

[llrs]

I'm not sure if I should increment the package version, let me know which version scheme do you want, or if I should move the bullet under the 1.2.0.9000 version comments.

[jennybc]

I'll merge and tweak the NEWS myself and tag you, so you see our style for future. I've made a note that we should clarify this in our contributing template. Which, ironically, this repo is not using itself! Will fix that too.

Thanks.

[llrs]

Yes, I looked for it but I couldn't find any contributing template (or code of conduct for what it matters).
Glad to help.