Because registry-url adds trailing slashes to registry URLs, update-notifier (and anything else using registry-auth-token) doesn't currently work with some registry/auth URLs.

Specifically, if the registry URL doesn't contain a trailing slash, like:
@myscope:registry=https://contoso.pkgs.visualstudio.com/_packaging/MyFeed/npm/registry

npm itself requires the following authToken line, due to its nerf-darting:
//contoso.pkgs.visualstudio.com/_packaging/MyFeed/npm/:_authToken=<auth_token>

But because registry-url appends a trailing slash, it makes the following registry url:
@myscope:registry=https://contoso.pkgs.visualstudio.com/_packaging/MyFeed/npm/registry/

which (when using a library like registry-auth-token / matching npm's behavior) doesn't work with:
//contoso.pkgs.visualstudio.com/_packaging/MyFeed/npm/:_authToken=<auth_token>

and instead requires
//contoso.pkgs.visualstudio.com/_packaging/MyFeed/npm/registry/:_authToken=<auth_token>

Note that registry-auth-token had buggy behavior as well, and in 3.1.1 just took the fix rexxars/registry-auth-token#10 to match npm's behavior.

Was there a reason for adding the additional trailing slash? There must have been since I see tests for it, but it seems wrong to do and is causing this failure.

Thanks.