internal: fix broken auth header provider
internal: fix broken auth header provider

Change I9cfd46787ebfb27cf2775dd3357eb26e089322a3 added
login.microsoft.net as a broken auth header provider. This was meant to
be login.windows.net. This change removes login.microsoft.net and adds
login.windows.net.

Change-Id: I6178053ab5c86b4f38996042384e1f4a139560aa
Reviewed-on: https://go-review.googlesource.com/47250
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

golang/oauth2